A: Excuse me. Can you help me?
打扰下，你能帮助我吗？

B: Certainly. What can I do for you?
当然可以，你需要什么？

A: I need to purchase a sweater.
我需要买件毛衣。

B: What is your size?
你穿多大尺寸的？

A: Medium should be fine.
中号就行了。

B: Is this one okay?
这件行吗？

A: Hmm. Can I try it on somewhere?
我能试穿下吗？

B: The fitting room is in the left corner.
试衣间在左边的拐角。