What is the primary difference between a Lookup relationship and a Master-Detail relationship?

Correct answer: Master-Detail enforces deletion; Lookup does not

Option A is correct because in a Master-Detail relationship, deleting the master record automatically cascade-deletes all related detail records, enforcing tight ownership, whereas in a Lookup relationship the related record is not deleted when the parent is deleted, making it a softer, optional association. Option B is incorrect because it is the reverse of reality; in a Master-Detail relationship the master field on the child is required, while a Lookup field is typically optional. Option C is incorrect because Master-Detail does not make records read-only; it controls ownership, sharing, and roll-up summary fields, not field editability in that sense. Option D is incorrect because a junction object with two Master-Detail relationships is the Salesforce pattern for many-to-many, while a single Lookup relationship does not inherently support many-to-many either.