These achievements_______ without the contribution of Qian Xuesen, a key leader of the New

China's nuclear, missile and so on.  [ ]

A. would have been unthinkable

B. would not be unthinkable

C. would be unthinkable

D. would not have been unthinkable

容积式流量计在安装时，下列正确的是（）。

A、无要求，随意安装

B、只对直接管段有要求，对流向无要求

C、不需要加过滤器

D、安装时应使流体流动方向与流量计的流向标志一致