A:cook
B:cooks
C:to cook
甲地高出乙地500米,乙地的海拔是1000米,则甲地的海拔是( )
No one was allowed to leave the lab without the professor's p____.
抄写下列句子。
①Time for music class.
②It's 8 o'clock .It's time for English class.
③Hurry up .It's time to go to school.
④It's 9:00 .It's time to go to bed.
在人体的结构层次中,皮肤属于( )