The correct option is E Either only III or only I and II
From I, we conclude that the girl is either Kunal's or his brother's wife. But, according to II, Kunal has no siblings.
So, from both I and II, we conclude that the girl is Kunal's wife.
From III, we find that the girl is the only daughter-in-law of Kunal's mother i.e. she is Kunal's wife.