按要求改写下列各句，每空一词。

1. She has lunch at twelve. (对划线部分提问)

   _____ _____ does she have lunch?

2. What time is it now? (改为同义句)

   _____ the _____ now?

3. Jack eats breakfast at home. (改为一般疑问句)

   _____ Jack _____ breakfast at home?

4. Scoot works very long hours every day. (改为否定句)

   Scoot _____ _____ very long hours every day.

5. Thanks for your letter. (改为同义句)

   _____ _____ for your letter.

网络安全技术的研究主要涉及三方面问题： 【2】 、安全机制和安全服务。