Using Process Builder on Opportunities and a Chatter post action, and enabling Feed Tracking on Opportunities are two configurations that an app builder can recommend to meet the requirement of notifying and tracking changes to an Opportunity Close Date. Process Builder can create a process that triggers a Chatter post action when the Close Date field is changed on an Opportunity. Feed Tracking can enable tracking of field history for the Close Date field on the Opportunity feed. Creating an Opportunity outbound message and activating Historical Trending for Opportunities are not valid configurations for this requirement.

The solution that the app builder should use to meet DreamHouse Realty's needs is Master-Detail Child Object. A master-detail relationship can be used to create a parent-child relationship between two objects, where the child records inherit the sharing and security settings of their parent record. The app builder can create a roll-up summary field on the parent object to calculate the highest value of all child records. Option B is incorrect because Text Area (Long) is a field type that allows users to enter up to 131,072 characters on one line, which is not suitable for this requirement. Option C is incorrect because Multi-select Picklist is a field type that allows users to select multiple values from a predefined list, which is not suitable for this requirement. Option D is incorrect because Lookup Object is not a valid term, but rather Lookup Relationship, which is a type of relationship that links two objects together, but does not support roll-up summary fields.

The two considerations that should be made are: The Star records are all required to have an existing value in their Galaxy field. This is a prerequisite for converting a lookup relationship to a master-detail relationship. A lookup relationship is an optional relationship that links two objects together, but does not enforce referential integrity or cascade delete. A master-detail relationship is a required relationship that links two objects together and enforces referential integrity and cascade delete. To convert a lookup relationship to a master-detail relationship, all child records must have a value in their lookup field that references an existing parent record. The Galaxy object has fewer than two existing master-detail relationships. This is another prerequisite for converting a lookup relationship to a master-detail relationship. An object can have up to two master-detail relationships with other objects and can act as both the parent and child in different relationships. To convert a lookup relationship to a master-detail relationship, the parent object must have fewer than two existing master-detail relationships with other objects. The Galaxy object is required to contain existing roll-up summary fields is not a valid consideration, as it is not related to converting a lookup relationship to a master-detail relationship.

The app builder should use the CASESAFEID(Id) formula to create this new field. The CASESAFEID function returns the 18-digit case-insensitive version of the record ID, which is unique for each record in Salesforce. The 18-digit record ID is useful for exporting data to external systems that require case-sensitive IDs1. Option A, C, and D are not formulas that can return the 18-digit record ID.

* C: Setting the component visibility based on an advanced filter type, using the contact field(s) to define dynamic criteria, allows displaying information relevant to specific account conditions without needing user interaction.References:
* Salesforce Help - Dynamic Forms