情景对话。

A: Hi I am Wang Hong. I am a journalist from Taiyuan TV Station. I want to know something about

    your school life. Could you 1______ about it?

B: Yes, I'd love to. 

A: Well, 2______

B: About two thousand students in our school. 

A: And are you always busy with your lessons?

B: 3______ We have much homework to do every day. We have to work hard. 

A: What about your free time?

B: We can take part in different kinds of activities. 4______ in our school. And these hobby groups

    are open to us on Friday afternoons.

A: I think your school is wonderful, isn't it?

B: I think so.

A: It's nice talking to you. 5______

B: You're welcome.

ITSEC的功能要求不包括以下（）方面的内容。

A.机密性

B.完整性

C.可用性

D.有效性