下图为世界局部地区年平均气温等温线图，完成下题。

小题1:造成①处气温与同纬度地区明显不同主要因素是

A．海陆

B．洋流

C．太阳辐射

D．大气环流小题2:图中四个区域，南北温差最小的是

A．甲

B．乙

C．丙

D．丁

  The teacher tells his students to read the novel over and over again until they ______ it.

A．understand 　

B．understood

C．have understood

D．have been understood