Universal Containers needs to create a roll-up summary field on a custom object that counts the number of related records on another custom object. What type of field must exist before the roll-up summary can be created, and where should it be located?

A. A lookup relationship field on the parent object.
B. A lookup relationship field on the child object.
C. A master-detail relationship field on the parent object.
D. A master-detail relationship field on the child object.

Suggest answer: D

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