回答：1.I wonder whom he is talking to on the phone.
2.Please tell me how you worked out the math problem.
3.You must explain to us why you have changed your mind.
4.Do you know who will be our English teacher next term?
5.There are so many good books on it,and I don’t know which is better.
6.It is getting dark,but he hasn’t turned up yet; we doubt if he will come as he promised.
7.Think it over and let me know whether you agree with me.
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