The correct answers are A. Use a master-detail relationship between the Park and Trail objects and C. Use a roll-up summary field on the Park record to show the total number of trails .

To show the total number of child Trail records on the parent Park record without code, the app builder should use a roll-up summary field . Salesforce documentation states that roll-up summary fields display values on a master record based on related detail records.

That means Park should be the master object and Trail should be the detail object. Then a roll-up summary field on Park can count the related Trail records.

B is incorrect because standard lookup relationships do not support roll-up summary fields.

D is incorrect because a formula field cannot count multiple child records.

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