A:it's really a nice day today, isn't it?
B:what knid of weather are we going to have today?
C:do you think it is going to rain today?
D:what' it like outside today?
一列火车长120m,匀速通过长360m的山洞,从火车进洞到车尾离洞共用1min,火车行驶的平均速度是( )