A:was the teacher; did he care
B:was the teacher; he cared
C:the teacher was; did he care
D:the teacher was; he cared
两列火车,甲车每秒钟行20公尺,乙车每秒行12公尺,当车尾相齐,甲车尾越过乙车头时耗时30秒,车头相齐,甲车尾越过乙车头时耗时40秒,则甲、乙车身长各为几公尺?
回答下列问题:
读青藏地区图完成下列各题: