A:You can carry one piece.
A: 您只能带一件行李。
B:What about the other one?
B：另外一件行李怎么处理?

A:How much luggage can I carry on?
A: 允许随身携带几件行李?
B:You can carry one piece.
B：您只能带一件行李。

重点讲解：

You're only allowed to carry one piece of luggage.
You can carry one piece.
机场安检时，经常会听到工作人员说，"您只能带一件行李"，这句话表示成 You're not allowed to carry one piece of luggage.并没有错误，但是老外常简单地说：You can carry one piece.需要注意的是，在表示一件行李时，要用one piece of luggage。