电动机保护用断路器可分为两类：①断路器只作保护而不担负正常操作；②断路器兼作保护和不频繁操作之用。
参考答案：对
一种饮料，零售每瓶卖2元，商场为感谢广大顾客对该产品的厚爱，特开展“买五赠一”大酬宾活动，商场的做法优惠了（ ）%。
She first met Peter four years ago, and he______ at a computer store at that time. [ ]
A. has worked
B. had worked
C. was working
D. had been working
