The correct answer is A. finished.
The sentence “We finished our breakfast half an hour ago” is in the simple past tense. The simple past tense is used to talk about events that happened at a specific time in the past. In this case, the event is “finishing breakfast” and the time is “half an hour ago”.
The other options are not correct because they are not in the simple past tense. Option B, “have finished”, is in the present perfect tense. The present perfect tense is used to talk about events that happened at an unspecified time in the past or that have a connection to the present. In this case, the event is “finishing breakfast” and there is no connection to the present, so the present perfect tense is not appropriate. Option C, “had finished”, is in the past perfect tense. The past perfect tense is used to talk about events that happened before another event in the past. In this case, there is no other event in the past, so the past perfect tense is not appropriate. Option D, “none of these”, is not correct because one of the options is correct.
I hope this explanation is helpful. Please let me know if you have any other questions.