As nobody here knows what is wrong with the machine, we          send for an engineer to handle the problem．

A．should

B．must

C．can

D．would

下述关于低温哪些是正确的（）

A.30～28℃属于中度低温范围

B.体外循环心内手术常用中度低温

C.20℃以下为深度低温

D.深低温常用于复杂心脏手术

E.低温常用于冠状动脉搭桥术