Mr. Smith has bought a new house in the country, around _____ some green trees.

A．which is

B．it is

C．which are

D．them are 

关于VA/Q比值哪一项是正确的（）。

A.vA/Q比值为0.8

B.正常直立位时肺顶部VA/Q为0.83。肺底部为0.33

C.正常直立位肺部从上到下，VA/Q值由小变大

D.全部VA/Q是肺中央VA/Q比值

E.单肺通气不会使VA/Q比值失调