Answer:
D Michelle’s birthstone is a diamond; Debra’s is an opal.
Step-by-step explanation:
Semicolons serve to link two independent clauses (clauses expressing complete thoughts on their own) with closely related ideas that are not joined by a conjunction such as but, and or, nor, for, yet, or so.
Option D is the correct answer because the clauses Michelle’s birthstone is a diamond; Debra’s is an opal are two independent clauses whose ideas are closely related to each other and that are not joined by a coordinating conjunction.