吸收塔充液前，（）应投入正常运行。
A.闭路循环水系统
B.蒸氨器
C.氧化还原反应器
D.排酸泵
参考答案：A
— I went to Tom's birthday party last night. A lot of my good friends were there too.
— It ________ fun. [ ]
A. must be
B. can be
C. must have been
D. can have been
对网络故障进行判断时，在发现网络故障之前应该做的工作有哪些（）
A.了解网络拓扑关系
B.日志和笔记
C.贴上标签
D.寻找最近的修改
