根据对话内容，从下列选项中选出能填入空白处的最佳选项，其中有两个为多余选项。

— Hello. Gerry speaking.

— Hello, Gerry. It's me John here. ____ .

— Well, I'm terribly sorry, but I'm not feeling very well.

— Is that all?____

— No, I'm sorry. I was sick all night. I think it must be the fish I ate last night.

— Well, I think you should have at least phoned Kate and told her you weren't coming to the meeting.

— ____ I'm sorry about that. Anyway, I think I'll be able to get in to work tomorrow.

— ____ 

— I won't. Thanks for calling.

— ____.

A. Why didn't you phone?                 

B. OK. Take care and don't eat any more fish.

C. Why weren't you here at the meeting?      

D. That's all right.

E. We thought you might have had an accident or forgotten the day or something.

F. I'll be glad to see you again.          

G. Yes, I suppose I should have done so.

$a$ ．A课程成绩的频数分布直方图如下（数据分成6组： $40\le x<50$ ， $50\le x<60$ ， $60\le x<70$ ， $70\le x<80$ ， $80\le x<90$ ， $90\le x\le 100$ ）；

$b$ ．A课程成绩在 $70\le x<80$ 这一组是：

70  71  71  71  76  76  77  78  $78.5$    $78.5$   79  79  79  $79.5$

$c$ ．A，B两门课程成绩的平均数、中位数、众数如下：

根据以上信息，回答下列问题：

①求该束光线到AB的距离；

②试说明，入射光线经过折射后，直接照射到CB段弧面上的折射光线，不可能在CB段弧面上发生全反射．