Exam Certified Advanced Administrator topic 1 question 65 discussion

The question asks "What type of field"? Master-detail is not a field. Answer should be 'Roll-up Summary".

As this is about field and not relation then the answer is A

Master-detail is a type of field on the child object. The correct answer is C

The master here is Job Posting. The detail here is Job Application. The clue is you're calculating how many job applications per job posting. Master-detail relationship field is created on the detail record. Roll-up summary would be needed yes to do the calculation required, but that would go on to the master record - i.e. the Job Posting record.

Why not B?

The correct answer is Master Detail. You can only create a MD on the child object, which in this instance is the Job Application custom object. Then you can create a Roll-up summary on the master, which is the Job Posting custom object. The key is the ability to identify which is the Master and child.

To make the Job Application a child of the Job Posting and allow for roll up summaries to be created on the Job Posting, you need to first create a Master Detail relationship between the two objects. The MD relationship needs to be on the child object so that its values can be related (and controlled) by the Parent.