--Why you came back to town?

(traditional) 你 怎麽 回城/回來 了？

(simplified)  你 怎么 回城/回来 了？

* why 爲什麽，怎麽(in speaking)//为什么，怎么

town,city 城市

--Tomorrow is my friend's birthday. I want to surprise her.

(traditional) 明天 是 我 朋友的 生日，我 想 給她 一個 驚喜。

(simplified)  明天 是 我 朋友的 生日，我 想 给她 一个 惊喜。

* surprise n. 驚喜/惊喜 (surprise:驚/惊  very happy,ecstatic:喜)

surprise