Answer:
The answer is explained below.
Step-by-step explanation:
Option A is incorrect because the sentence is passive: the subject, the store, doesn't perform the action but receives it.
Option B is correct because the sentence could be expressed as Somebody robbed the store just after midnight. By using an indefinite pronoun, we express that we don't know who did it.
Option C is incorrect because as seen in the previous explanation, this sentence can be expressed in active voice.