---Do you know how long ________?  ----I’m sorry I don’t know.

A．he has come here

B．has he been married

C．Tom has bought the car

D．his uncle has been abroad

双作用叶片泵从转子（）平衡考虑，叶片数应选（）；单作用叶片泵的叶片数常选（），以使流量均匀。

A、轴向力、奇数、偶数

B、径向力、偶数、、奇数

C、轴向力、偶数、奇数

D、径向力、奇数、偶数