水文资料的主要来源是（）对各项水文要素的长期观测。
A.水文测站
B.水文局
C.水利局
D.气象站
参考答案：A
You ____ all those clothes! We have a washing machine to do that sort of thing. [ ]
A. needn't have washed
B. shouldn't have washed
C. must not have washed
D. can not have washed
操作液压油管钳不论上扣卸扣，挂挡顺序都要遵循（）的原则。
A.“高一低一低”
B.“低一低一高”
C.“低一高一低”
D.“高一高一低”
