用括号里所给动词的适当形式填空。
(1)He often ____ (study) with his friends in the library after class.
(2)We should do more exercise ____  (keep) healthy.
(3)These magazines must not ____  (take) out of the reading room.
(4)  I called you this morning, but nobody answered it.
     Oh, we ____ (run) in the park.
(5)Jacky Chen ____  (star) in many action films for many years. I admire him very much.

读“世界海陆分布图”，完成下列各题

（1）据图观察，陆地主要集中在____ 半球（北或南）；
（2）中国位于A：____ 洲，它是世界面积最大的洲，它与B洲的分界线是____ ；
（3）世界面积最大的洋是____ ，跨经度最广的洲是____ （填字母）。

东北地区的中学生寒假时间很长，主要原因是 (    )

关于电磁波，下列说法错误的是（　　）