某成像系统能提供的灰度级数为256，其比特数为（）. A.1 B.3 C.8 D.1

A. I have to study hard now. B. No, you needn’t. I just went to bed late last night. C. Yeah. I’ll never do that again. D. I have a pain（疼痛） in my head. E. You’d better learn from others. F. Oh, no. I have to stay up again. G. Thanks a lot.

A: Tom, you look tired today. Are you all right?
B:   小题1:  .
A: Sorry to hear that. I’ll phone the doctor.
B:   小题2: . I was getting ready for the coming exam.
A: You’d better go to bed earlier tonight.
B:  小题3: . Because I don’t have enough time to go over all the subjects.
A: Why? Must you study that way? It is bad for your health.
B: But I played too much last month.  小题4: .
A: I see, Tom. You’ve learned something from the past, haven’t you?
B:   小题5:  .
A: Good. I believe（相信） you.