______ of the land in that district _______ covered with trees and grass.

A．Two fifths; is

B．Two fifth; are

C．Two fifth; is

D．Two fifths ; are

轮对相对构架的自由横动量1、3、4、6、位为（）mm。

A、12～22

B、10～20

C、15～22

D、36～46