In which situation is the past perfect tense primarily used?

The past perfect tense is used to indicate that an action was completed before another action took place in the past. This is important for providing clarity in sequences of events; it allows a speaker or writer to establish a timeline. For example, if someone says, "I had finished my homework before I went out," it emphasizes that the homework was completed prior to going out, clarifying the order of events.

In contrast, the other options do not align with the primary use of the past perfect tense. Ongoing actions are typically described using the present continuous or past continuous forms. Future plans would use the simple future or future continuous tense rather than the past perfect. Finally, asking questions about the past can be conducted in several tenses, but it typically does not require the past perfect, as it doesn't focus on the order of completed actions as indicated by the past perfect tense.