a) Because Vrtrasura was the son of Tvasta who was a great devotee
b) Because Vrtrasura was the brother of Vishvarup
c) Because Vrtrasura was King Citraketu in his previous birth who was then a great devotee
d) None of the above
The correct answer is
c) Because Vrtrasura was King Citraketu in his previous birth who was then a great devotee