下列选项关于群落的说法正确的是( )
A:出生率
B:性别比例
C:分层结构
D:年龄结构
Jack hurried to the rail way station in a taxi this morning ____ ____he wouldn't miss the train to Tianjin.
下列说法正确的是( )
If you lost the book in the library, you must it.