AHSME 1967 Problem 1

The three-digit number $2a3$ is added to the number $326$ to give the three-digit number $5b9$. If $5b9$ is divisible by 9, then $a+b$ equals $\text{(A)}\ 2 \text{(B)}\ 4 \text{(C)}\ 6 \text{(D)}\ 8 \text{(E)}\ 9$