非上市证券是指经证券主管机关核准发行,并经证券交易所依法审核同意,允许在证券交易所内公开买卖的证券。( )
A.
B.
C.
参考答案:B
心力衰竭引起的发绀属于()
A.混合性发绀
B.心性混合性发绀
C.肺性发绀
D.缺血性周围发绀
E.淤血性周围发绀
The shear rams of a ship blowout preventer stack are used in emergency well control to().
A.close and seal around the drill pipe
B.close and seal around casing
C.cut off pipe inside the preventer stack
D.close and seal around drill collars