Chapter 5, Problem 113SAE

What is the simplest ratio a:b when the equation below is property balanced?
${\text{a CIO}}^{\text{-}}\left(\text{aq}\right){\text{+bI}}_{\text{2}}\underset{\text{solution}}{\overset{\text{acidic}}{\to }}{\text{cCI}}^{\text{-}}\left(\text{aq}\right){\text{+dIO}}_{\text{3}}^{\text{-}}\left(\text{aq}\right)$
a. 2:5;
b. 5:2;
c. 1:5;
d. 5:1;
e. 2:3;