What is the tense of the sentence "The teacher asked when he wasn't working on his project."?

The tense of the sentence "The teacher asked when he wasn't working on his project" is indeed Past Continuous. This is because the phrase "wasn't working" indicates an ongoing action that was happening at a specific point in the past. The structure of the Past Continuous tense is formed by using "was" or "were" alongside the present participle (the -ing form) of the verb.

In the context of the sentence, it implies that at the time the teacher was asking, there was a period in the past where the subject was in a state of not working on the project. This continuous nature reflects an action that was ongoing during that time frame.

The other options do not apply here. Present Simple would suggest a habitual or general action rather than a specific past occurrence that involved an ongoing action. Future Simple discusses actions that will happen later, which doesn't fit the context of a past inquiry. Past Perfect is used to describe an action that was completed before another action in the past, which is also not relevant in this case. Thus, the use of Past Continuous aptly conveys the meaning and timing of the actions described in the sentence.