This question assesses the understanding of the past perfect tense, which is used to indicate that an action was completed before another action in the past. The correct answer is B. She had finished her homework before the movie started., as it correctly uses the past perfect tense ('had finished') to indicate that the homework was completed before the movie started. A. is incorrect because it uses the present perfect tense ('has finished') which is not appropriate for indicating an action completed before another past action. C. is incorrect because it reverses the order of actions, suggesting the movie started before the homework was finished. D. is incorrect because it uses the present tense, which does not indicate a sequence of past actions.