利用重力原理进行膝关节灌注时,为了保证视野清晰,进出水管的管径必须保证在:()
A.4~5mm
B.5~6mm
C.5~7mm
D.6~8mm
参考答案:C
There is _____________ old man at home. [ ]
A. a
B. an
C. the
x=7是方程25-3x=4的解.______.(判断对错)