The correct answer is C. Custom object with Master-detail field to Opportunity.

AW Computing needs many help requests related to one Opportunity, so the help request should be a custom child object under Opportunity. Because the Opportunity page must show the most recent request date, the app builder needs a Roll-Up Summary field on Opportunity using MAX on the request date field.

Salesforce roll-up summary fields work on the master side of a master-detail relationship, and MAX can be used for date/date-time fields.

A is backward because the master-detail field belongs on the child object, not Opportunity.

B and D use lookup relationships, which do not support standard roll-up summary fields.

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