当注水量小且扬程较高，离心泵机组（）较低。
A.排量
B.扬程
C.效率
D.电流
参考答案：C
—This pair of shoes belong to Jack. He likes this kind very much.
—It __ be his. It's too large for him. [ ]
A. can; can't
B. may; needn't
C. must; mustn't
D. must; can't
氧化风机入口过滤器太脏，会导致氧化风机运行电流大大降低。（）
