—The scarves are all beautiful.I can't decide which one to choose.—Oh,look at this red one.I think it's______.

下图为一幅等值线图，a、b分别为等值线的数值（a＞0，b＞0），据此回答下列各题。

Now more and more workers ______their free time trying to improve themselves at school or college.

地球外圈分为四圈层，即____、____、____和____。