管路系统的特性曲线是随着（）的增加而上升。
A、流量
B、扬程
C、轴功率
D、效率
参考答案：A
什么是女性青春期发育过程中的里程碑（）。
A. * * 发育
B.音调变高
C.出现阴毛、腋毛
D.月经来潮
E.排卵
— Thanks a lot, Mr. Wang. I don't know how to ________ the help you gave me during my stay here.
— It's my pleasure. Welcome to China again when you have time. [ ]
A. pay off
B. pay back
C. pay for
D. pay to
