They ----- (live) in this house since 1987.a.are livingb.have been livingc.may lived.can be living

The correct answer is "b. have been living." Here's the step-by-step explanation:

1. The sentence states that the action of living in the house started in 1987 and is still ongoing. This indicates a continuous action that started in the past and continues into the present.
2. The present perfect continuous tense is used to express an action that started in the past, is still happening in the present, and may continue into the future.
3. The correct form of the present perfect continuous tense is "have been + present participle (-ing form of the verb)."
4. Therefore, the correct answer is "b. have been living."