--- Did you telephone Uncle Sam our plan for the Christmas holidays on his farm?

--- Yes, he was happy about our arrival, and he eagerly asked when ______.

A．has we arrived

B．we had arrived

C．were we arriving

D．we were arriving

为了保护数据库的安全，主要在（）几个层次上采取安全性措施。
Ⅰ．数据库系统层Ⅱ．物理层Ⅲ．操作系统层
Ⅳ．人员层Ⅴ．网络层

A.Ⅰ和Ⅱ

B.Ⅰ、Ⅳ和Ⅴ

C.Ⅲ、Ⅳ和Ⅴ

D.都是