根据所给情景，从A、B、C三个选项中选出最佳选项。

1. — Can I take this seat?

    — _______. It's for our teacher, Mr Li. [ ]

A. Of course

B. You'd better not

C. Yes, please

2. — You speak English well.

    — _______. [ ]

A. Don't say so

B. Just so-so

C. Thank you

3. — There's going to be an exciting basketball match in our school.

    — _______ I can't wait. [ ]

A. It's boring.

B. What a pity!

C. That's great.

4. — I have to make a speech at a meeting. I feel nervous about it.

    — _______. I'm sure you can do it well. [ ]

A. Take it easy

B. Don't be so sad

C. That's all right

5. — What do you think of the math problem?

    — _______. All of us can work it out. [ ]

A. It's a piece of cake

B. It's difficult

C. I hope so

设有图书管理数据库：
图书(总编号C(6)，分类号C(8)，书名C(16)，作者C(6)，出版单位C(20)，单价N(6，2))读者(借书证号C(4)，单位C(8)，姓名C(6)，性别C(2)，职称C(6)，地址C(20))借阅(借书证号C(4)，总编号C(6)，借书日期D(8))
对于图书管理数据库，分别求出各个单位当前借阅图书的读者人次。下面的SQL语句正确的是______。
SELECT单位，______FROM借阅，读者
WHERE：
借阅.借书证号=读者.借书证号______。

A．COUNT(借阅.借书证号)GROUP BY单位

B．SUM(借阅.借书证号)GROUP BY单位

C．COUNT(借阅.借书证号)ORDER BY单位

D．COUNT(借阅.借书证号)HAVING单位