The correct answer is D. Nephew.
Deepak’s father’s wife is Deepak’s stepmother. The daughter of Deepak’s stepmother is Deepak’s stepsister. The younger of the two brothers of Deepak’s stepsister is Deepak’s nephew.
A son is a male child of a parent. A brother is a male sibling. A cousin is a person who is related to another person through the parents or grandparents of either person. A brother-in-law is the husband of one’s sister or brother.