Student or Learner
1. A：Can you tell me what he looked like？
B：Oh，he _______ about 55, and he was tall with grey hair.
The given answer is "must/might have been". I would think "may/could have been" are fine too. Am I right?
2. I didn't sleep well. There was a lot of noise. It _____ have been the
The given answer is "must/might/could". Comparing the given answers with those to the last question, I feel more puzzled. Why can't "may" be used in this sentence?
Could I ask native speakers to help me please? Thank you in advance.