The past perfect tense is used to indicate an action that was completed before another action in the past. Option B correctly shows this, as the task was completed before the deadline. Therefore, B is correct. * **Core concept**: Correct application of the past perfect tense, forming 'had + past participle'. * **Solution analysis**: The past perfect is for actions that occurred before another point in the past. Option B provides a situation in the past (deadline) and an action completed before this point in time. Therefore B is the only correct usage. * **Option A Analysis**: Incorrect because it is a future perfect tense. * **Option C Analysis**: Incorrect because it uses the present continuous future tense. * **Option D Analysis**: Incorrect because it uses present continuous tense. * **Easy mistake**: Confusing different past tenses or using future tenses incorrectly.