用所给单词的适当形式填空。

1. The old in the home for the elderly _____ (take) to the hospital for medical

research once a year.

2. He started _____  (tell) me about all of the chores he _____ (have) to do.

3. Mike, would you like _____ (feed) my cat when I leave home?

高频开关电源的二次下电功能的作用是（）。

A．避免蓄电池组过放电

B．保护整流器

C．切断部分次要负载，延长重要负载的后备时间

D．发出电池电压低告警