Answer:
Option (C)
Explanation:
Two ratios are proportional when one is a multiple of the other.
Consider A: 1 : 3 and 6 : 3
6 : 3 is equivalent to 3(2 : 1). 1 : 3 and 3(2 : 1) are not proportional.
Consider B : 1 : 3 and 3 : 6.
3 : 6 is equivalent to 3(1 : 2).
Again the two ratios are not proportional.
Now for Option C : 3 : 1 and 9 : 3.
9 : 3 is equivalent to 3(3 : 1). Clearly, the two ratios are proportional.
Hence, Option C is the answer.
For similar reasons Option D can be eliminated as well.