题目

---Do you know ______?   ---Sorry, but if he _____ back, I ____ you know as soon as possible.     A. when will he be back, comes, will let       B. when he will be back, will come, will let    C. what time will he be back, will come, let    D. what time he will be back, comes, will let 答案：B在下列各数中，无理数是A．-2.1 B． C．π D．