In therory the amount of tips is optional, but in many places of Ameica, there are some unwritten rules on tipping.

理论上小费给多少纯属自愿，但是在美国，不少地方都有不成文的规矩。

youdao

In therory the amount of tips is optional, but in many places of Ameica, there are some unwritten rules on tipping.

理论上小费给多少纯属自愿，但是在美国，不少地方都有不成文的规矩。

youdao