SObject Collections is a REST API composite resource that allows you to create, update, or delete up to 200 records in one API call. You can specify the type of operation (create, update, or delete) for eachrecord in the request body, andthe response body will contain the status and IDs of each record. SObject Collections is suitable for bulk operations on records that are not related to each other1.

SObject Tree is another REST API composite resource that allows you to create up to 200 records in one API call. However, unlike SObject Collections, SObject Tree requires the records to be related to each other in a hierarchy. You can specify the parent and child records in a JSON tree structure, and the response body will contain the reference IDs and URLs of each record. SObject Tree is suitable forcreating nesteddata in one request2.

Batch is a REST API composite resource that allows you to combine up to 25 requests in one API call. Each request can be a different type of operation (query, create, update, delete, etc.) on different objects. The response body will contain the status and results of each request. Batch is suitable for grouping multiple requests into one transaction3.

Composite is a REST API composite resource that allows you to execute aseries of REST API requests in one API call. You can use the output of one request as the input of another request using a reference ID. The response body will contain the status and results of each request. Composite is suitable for chaining requests that depend on each other.

Therefore, the correct answer is A, because SObject Collections is the only REST API composite resource that allows bulk updates on records that are not related to each other.