Answer:
C is the answer
3 :1 and 9 :3
Explanation:
a :b :: c:d =
=

3 :1 and 9 :3
=
and

3:1 :: 9:3 =
=

3 = 3 so these two ratios are proportional
or another method is find the cross multiplication

i.e 3 × 3 = 9 × 1
9 =9
so these two ratios are proportional