The correct option is
C Asked
The given sentence is in past tense, it describes events that have already happened. We can conclude this from the given words "when...were over" where 'were' is an auxiliary verb that expresses the past tense.
Option B: 'Asked' is a past participle that expresses the simple past tense. It explains an event that completed in the past 'had asked'. Hence option B is correct.
Option A: 'Asks' expresses the simple present tense and describes an event that takes place on a daily basis. It does not express the required past tense here.
Option C: 'Had' in 'had asked' expresses the past perfect tense. The past perfect tense describes an action that completed before another action took place.
The given sentence simply states one action 'asked' and does not indicate the beginning of any other action. Hence the past perfect tense is not applicable here.
Option D: 'Would ask' expresses a hypothetical event, in which an action may or may not take place. But, the action in the passage has already happened. Hence these options are wrong.