句型转换。

1. Is that his book? (改为复数句) 

                              their books?

2. He plays volleyball on Saturday afternoon. (改为一般疑问句). 

                 he              volleyball on Saturday afternoon?

3. They like broccoli and strawberries. (改为否定句).

    They                           broccoli or strawberries.

4. Nick usually eats breakfast at 7:00 every morning. (对划线部分提问) 

                 does Nick usually              at 7:00 every morning?

5. My favorite color is red. (对划线部分提问). 

                              is your favorite color?

某Web 网站向CA 申请了数字证书。用户登录该网站时，通过验证 （） ，来确认该数字证书的有效性，从而 （） 。

用户登录该网站时，通过验证（）

A．CA 的签名

B．网站的签名

C．会话密钥

D．DES 密码