---Whose dress is this?

问的是谁的衣服,你只要答是谁的就好.比如我的:It's mine.

这是谁的连衣裙？
It's hers.

dress:女服（主要是连衣裙）, 童装, 服装, 衣服

It's his(or hers).

this dress is mine./this is my dress.

It's sb's