2.back and forth 往返,来回
典例
The bus runs back and forth between the airport and
the downtown area.巴士往返于机场与市中心之间。
拓展
back to back 背靠背
get one's back up 令某人不快 get off one's back 不再找某人麻烦 have one's back to the wall 处境困难 put one's back into 非常努力地做