There are a lot of computers in the lab and they need professionalto make sure they can be

问题补充：

There are a lot of computers in the lab,and they need professionalto make sure they can be in a good state.

A. operation

B. maintenance

C. service

D. advice

答案：

A. operation

(答案→)B. maintenance

C. service

D. advice

解析：maintenance保养；operation操作；service服务；advice建议。