Pointing towards a boy, Veena said "He is the son of only son my grandfather." How is that boy related to Veena?

It must be D since Veena grandfather must not necessarily be her father’s father.

I don't agree with Examveda team...The Answer is none of these(E)...coz boy is either veena's couzin or brother...the question says boy's father is only son of veen's grandfather(not only child)..there is possibility that boy's father has so many sisters as well and veena is the daughter of one among them..
The fact here is only son(means having female siblings as well).Not only child(either son or daughter without siblings)
Hope this may help u..Thank u

Tge correct anwer is (E) None of these...

I dont agree with ur answer....Only son and only child are two different terms.only son means having many sisters as well and only child means either son or daughter with no siblings..Here if boy is the son of veen's garandfather's only son then either veena is daughter of boy's father or his father's sister's daughter....here veena is either couzin or sister of boy...so approprate answer was either couzin or brother...but we dont have this option...so correct answer is (D)

I did not understand
Can you please explain properly?