大气层中又分许多气层，请将下列四种气层依高低排列A.平流层 B.对流层 C.中气层 D.电离层
参考答案：
DCAB
— Oh, that's just my missing pen. Where on earth was it?
— It _____ off the table into the corner. [ ]
A. has fallen
B. fell
C. falls
D. was falling
正常人腹部外形通常描述为（），当出现明显（）或（）时，则应视为异常。
