只有当市电中断或低于（）时，UPS电源才会向负载提供稳压、稳频的交流电。

A、120V

B、170V

C、220V

D、380V

• (A) 条件(1)充分，但条件(2)不充分．
• (B) 条件(2)充分，但条件(1)不充分．
• (C) 条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
• (D) 条件(1)充分，条件(2)也充分．
• (E) 条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分．

One hundred cars on a particular lot were available with a compact disc player, a car phone, or both. How many cars had only a car phone
(1) The number of cars with compact dise players was twice the number of cars with both a compact dise player and a car phone.
(2) Thirty cars had both, which was half the number of cars with compact disc players.