n.

1. 两匹马前后纵列拉的双轮马车
2. 串座双人自行车
3. 两个以上前后排列的人（或物）

ad.

1. 一前一后地

a.

1. 一前一后的；串联的；前后有座位的

n.

1. a bicycle with seats and pedals for two riders, one behind the other.
2. a carriage driven by two animals harnessed one in front of the other.
3. a group of two people or machines working together.

adv.