结冰河流测流次数的分布,应以控制()变化过程为原则。
A、冰厚
B、断面冲淤
C、断面流量
D、冰期改正系数
参考答案:B, C, D
Frank , with his two sisters , _____ London by train which _______ at 8:30 next morning .
A.is leaving for ; will leave
B.are leaving for ; leaves
C.is leaving for ; leaves
D.will leave for ; will leave
简述双作用叶片泵的工作原理。