余热锅炉干锅的现象有（）。
A、汽包低液位报警
B、液面计水位剧烈波动
C、炉水带油
D、主汽管内发生水击
参考答案：A
The students come to school early, but the teachers come ________.
A．much earlier
B．much early
C．more earlier
D．the earliest
蟑螂的栖息习性有哪些？
