Summer is _______ good time for swimming, so you can find a good coach to help you in _______ summer of 2010.

A．a; the

B．/; /

C．a; /

D．/;the

起重机变换工作半径依靠变化起重臂的( )来实现的。

A．长度

B．方位

C．方向

D．角度