How many times is the word varna used in the Rig Veda in the sense of abirth-based social division?

How many times is the word varna used in the Rig Veda in the sense of

1.	How many times is the word varna used in the Rig Veda in the sense of abirth-based social division?
A.	ten
B.	five
C.	once
D.	nil
Answer» E.