往復的英文：
back and forth; to and fro
n. 后面，背面，反面；背，背部；靠背；后卫
v. 支持；后退，倒退；背书；下赌注于
adj. 背部的；后面的；过去的；拖欠的.
adv. 以前；向后地；来回地；上溯
Stand back to back!
背靠背站好！
They are on the back of the menu.
它们在菜单背面。
Our seats on the train were back to back.
我们在火车上的坐位是背靠背的。
adv. 向前，往外；（从...）以后
The forth day, the miracle seems hold forth.
第四天，奇迹似乎发生了。
A great epidemic burst forth.
突然发生了一场大瘟疫。
The tree branches forth in spring.
春天树木抽出新枝。
ad. 向后,向那边
The ship was rolling heavily to and fro.
轮船剧烈地颠簸。
He was bowing to and fro.
他一个劲儿地点头哈腰。
The tall chimney tottered(to and fro) and then collapsed.
那座高烟囱摇摇晃晃地倒了下来.