Jody has 3 red marbles, 6 blue marbles, and 9 yellow marbles. What is the ratio of red marbles to blue marbles?

A.
3:6
B.
3:18
C.
18:3
D.
6:3

The ratio of red marbles to blue marbles is 3:6, which can be simplified to 1:2. Therefore, the answer is A. 3:6.