一般干管上每隔（）m应设置一个阀门，且设置在支管的下游为好。
A.200~400
B.400~600
C.600~800
D.800~1000
参考答案：B
-Did you attend Mary and Tom’s wedding ceremony?
-Yes，but as you know，they________each other no more than 3 months．
A．knew
B．had known
C．have known
D．have been knowr
EGR装置有何功用？
