The correct answer is D.
A search macro is a way to reuse a piece of SPL code in different searches. A search macro can take arguments, which are variables that can be replaced by different values when the macro is called. A search macro can also contain another search macro within it, which is called a nested macro1.
To represent an argument in a macro definition, you need to use the dollar sign ($) character to enclose the argument name. For example, if you want to create a search macro that takes one argument named "object", you can use the following syntax:
[my_macro(object)] search sourcetype= object
This will create a search macro named my_macro that takes one argument named object. When you call the macro in a search, you need to provide a value for the object argument, such as:
my_macro(web)
This will replace the object argument with the value web and run the following SPL code:
search sourcetype=web
The other options are not correct because they use quotation marks (' or ") or percentage signs (%) to represent arguments, which are not valid syntax for macro arguments. These characters will be interpreted as literal values instead of variables.
Reference:
Use search macros in searches

Reference:
One of the statements that would help a user choose between the transaction and stats commands is that there is a 1000 event limitation with the transaction command3. The transaction command is used to group events that share a common value for one or more fields into transactions3. The transaction command has a default limit of 1000 events per transaction, which means that it will not group more than 1000 events into a single transaction3. This limit can be changed by using the maxevents parameter, but it can affect the performance and memory usage of Splunk3. Therefore, option C is correct, while options A, B and D are incorrect because they are not statements that would help a user choose between the transaction and stats commands.

The correct answer is C. Product, count: addtocart, count: remove, count: purchase, sum: addtocart, sum: remove, sum: purchase1.
In Splunk, the chart command is used to create a table or a chart visualization from your data2. The chart command takes at least one function and one field, and optionally another field to group by2.
In the given search, the chart command is used with two functions (count and sum), two fields (domain and price), and two fields to group by (product and action). The usenull=f and useother=f options are used to exclude null values and other values from the chart2.
The chart command creates a table with headers that match the order of the fields and functions in the command1. The headers for the count function are prefixed with count:, and the headers for the sum function are prefixed with sum:1. The values of the product and action fields are used as the suffixes for the headers1.
Therefore, the table headers created by this command are Product, count: addtocart, count: remove, count: purchase, sum: addtocart, sum: remove, and sum: purchase1.

https://docs.splunk.com/Documentation/Splunk/8.1.0/SearchReference/ConversionFunctions#tostring.28X.2CY.29 The tostring function in the eval command converts a numeric value to a string value. It can take an optional second argument that specifies the format of the string value. Some of the possible formats are:
hex: converts the numeric value to a hexadecimal string.
commas: adds commas to separate thousands in the numeric value.
duration: converts the numeric value to a human-readable duration string, such as "2h 3m 4s".
Therefore, the formats A, B, and D can be used with the tostring function.