we are not attacked by nuclear weapons, we promise that uncler no circumstances       use

the bomb first but we rescrve the right to use it for counter-attack when necessary.       [ ]

A. As long as; we shall      

B. If; shall we      

C. So long as; shall we      

D. Even if; we shall

梯形断面水渠按均匀流设计，已知过水断面A=5.04m²，湿周x=6.73m，粗糙系数n=0.025，按曼宁公式计算谢才系数C为（）。

A．30.80

B．30.13

C．38.80

D．38.13