The nested join is evaluated from the top to the bottom in the order of the ON conditions. This means that the join expression is formed by assigning each ON condition to the directly preceding JOIN from left to right.
The join expression can be parenthesized implicitly or explicitly to show the order of evaluation. In this case, the implicit parentheses are as follows:
SELECT * FROM (a INNER JOIN (b INNER JOIN c ON b~c = c~c) ON a~b = b~b) This means that the first join expression is b INNER JOIN c ON b~c = c~c, which joins the columns of tables b and c based on the condition that b~c equals c~c. The second join expression is a INNER JOIN (b INNER JOIN c ON b~c = c~c) ON a~b = b~b, which joins the columns of table a and the result of the first join expression based on the condition that a~b equals b~b. The final result set contains all combinations of rows from tables a, b, and c that satisfy both join conditions.
References: 1: SELECT, FROM JOIN - ABAP Keyword Documentation - SAP Online Help

You would use Access Controls with CDS Views for the following reasons:
* A. Only the data corresponding to the user's authorization is transferred from the database to the application layer. This is true because Access Controls allow you to define CDS roles that specify the authorization conditions for accessing a CDS view. The CDS roles are evaluated for every user at runtime and the system automatically adds the restrictions to the selection conditions of the CDS view.
This ensures that only the data that the user is authorized to see is read from the database and transferred to the application layer. This improves the security and the performance of the data access1.
* C. You do not have to remember to implement AUTHORITY CHECK statements. This is true because Access Controls provide a declarative and centralized way of defining the authorization logic for a CDS view. You do not have to write any procedural code or use the AUTHORITY CHECK statement to check the user's authorization for each data source or field. The system handles the authorization check automatically and transparently for you2.
The following reasons are not valid for using Access Controls with CDS Views:
* B. The system field sy-subrc is set, giving you the result of the authorization check. This is false because the system field sy-subrc is not used by Access Controls. The sy-subrc field is used by the AUTHORITY CHECK statement to indicate the result of the authorization check, but Access Controls do not use this statement. Instead, Access Controls use CDS roles to filter the data according to the user' s authorization2.
* D. All of the data from the data sources is loaded into your application automatically and filtered there according to the user's authorization. This is false because Access Controls do not load all the data from the data sources into the application layer. Access Controls filter the data at the database layer, where the data resides, and only transfer the data that the user is authorized to see to the application layer. This reduces the data transfer and the memory consumption of the application layer1.
References: 1: Access Controls | SAP Help Portal 2: ABAP CDS - Access Control - ABAP Keyword Documentation

The ABAP Cloud Development Model requires that only public SAP APIs and extension points are used to access SAP functionality and data. These APIs and extension points are released by SAP and documented in the SAP API Business Hub1. Customer-created function modules are not part of the public SAP APIs and are not released for cloud development. Therefore, calling a function module directly from an ABAP Cloud class is not allowed and will result in a syntax error. However, there are two possible ways to call a function module indirectly from an ABAP Cloud class:
* Create a wrapper class or interface for the function module and release it for cloud development. A wrapper is a class or interface that encapsulates the function module and exposes its functionality through public methods or attributes. The wrapper must be created in a software component with the language version set to "Standard ABAP" and must be marked as released for cloud development using the annotation @EndUserText.label. The wrapper can then be called from an ABAP Cloud class using the public methods or attributes2.
* Use the ABAP Cloud Connector to call the function module as a remote function call (RFC) from an ABAP Cloud class. The ABAP Cloud Connector is a service that enables the secure and reliable communication between SAP BTP, ABAP environment and on-premise systems. The function module must be exposed as an RFC-enabled function module in the on-premise system and must be registered in the ABAP Cloud Connector. The ABAP Cloud class can then use the class cl_rfc_destination_service to get the destination name and the class cl_abap_system to create a proxy object for the function module. The proxy object can then be used to call the function module3.
References: 1: SAP API Business Hub 2: Creating an ABAP Cloud Project | SAP Help Portal 3: Calling Remote Function Modules | SAP Help Portal

String functions are expressions that can be used to manipulate character-like data in ABAP. String functions can be either predicate functions or non-predicate functions. Predicate functions are string functions that return a truth value (true or false) for a condition of the argument text. Non-predicate functions are string functions that return a character-like result for an operation on the argument text1.
The following string functions are predicate functions:
* B. contains_any_of(): This function returns true if the argument text contains at least one of the characters specified in the character set. For example, the following expression returns true, because the text 'ABAP' contains at least one of the characters 'A', 'B', or 'C':
contains_any_of( val = 'ABAP' set = 'ABC' ).
* D. matches(): This function returns true if the argument text matches the pattern specified in the regular expression. For example, the following expression returns true, because the text 'ABAP' matches the pattern that consists of four uppercase letters:
matches( val = 'ABAP' regex = '[A-Z]{4}' ).
The following string functions are not predicate functions, because they return a character-like result, not a truth value:
* A. find_any_not_of(): This function returns the position of the first character in the argument text that is not contained in the character set. If no such character is found, the function returns 0. For example, the following expression returns 3, because the third character of the text 'ABAP' is not contained in the character set 'ABC':
find_any_not_of( val = 'ABAP' set = 'ABC' ).
* C. count_any_of(): This function returns the number of characters in the argument text that are contained in the character set. For example, the following expression returns 2, because there are two characters in the text 'ABAP' that are contained in the character set 'ABC':
count_any_of( val = 'ABAP' set = 'ABC' ).
References: 1: String Functions - ABAP Keyword Documentation

The possible replacements for "???" in the CDS view entity definition with an input parameter are A. built-in ABAP type and C. A data element. These are the valid types that can be used to specify the data type of an input parameter in a CDS view entity. A built-in ABAP type is a predefined elementary type in the ABAP language, such as abap.char, abap.numc, abap.dec, etc. A data element is a reusable semantic element in the ABAP Dictionary that defines the technical attributes and the meaning of a field12. For example:
* The following code snippet defines a CDS view entity with an input parameter currency of type abap.
cuky, which is a built-in ABAP type for currency key:
Define view entity Z_CONVERT With parameters currency : abap.cuky as select from ... { ... }
* The following code snippet defines a CDS view entity with an input parameter currency of type waers, which is a data element for currency key:
Define view entity Z_CONVERT With parameters currency : waers as select from ... { ... } You cannot do any of the following:
* B. A built-in ABAP Dictionary type: This is not a valid type for an input parameter in a CDS view entity. A built-in ABAP Dictionary type is a predefined elementary type in the ABAP Dictionary, such as CHAR, NUMC, DEC, etc. However, these types cannot be used directly in a CDS view entity definition. Instead, they have to be prefixed with abap. to form a built-in ABAP type, as explained above12.
* D. A component of an ABAP Dictionary structure: This is not a valid type for an input parameter in a CDS view entity. A component of an ABAP Dictionary structure is a field that belongs to a structure type, which is a complex type that consists of multiple fields. However, an input parameter in a CDS view entity can only be typed with an elementary type, which is a simple type that has no internal structure12.
References: 1: ABAP CDS - SELECT, parameter_list - ABAP Keyword Documentation - SAP Online Help
2: ABAP Data Types - ABAP Keyword Documentation - SAP Online Help