The correct answers are A. Roll-up summaries are limited to master-detail relationships and C. An object can have 25 roll-up summaries.

Roll-up summary fields summarize data from related child records onto the parent record, but standard Salesforce roll-up summaries are available only when the child records are directly related through a master-detail relationship. In this scenario, only one of the three custom objects has a master-detail relationship to Account, so native roll-up summaries cannot be used for the other two lookup/non-master-detail objects.

Salesforce also lists 25 roll-up summary fields per object as the standard allocation, so summarizing 15 fields from three objects would require 45 summaries, which exceeds the normal Account object limit.

B is incorrect because native roll-up summary calculations support COUNT, SUM, MIN, and MAX, not AVG.

D is incorrect because “20 object references” is not the key roll-up summary consideration in this proposal.