SMO 2008 Junior Round 1 Question 6

Question 6

In the following sum, $O$ represents the digit $0$. $A,B,X,Y$ represent distinct digits. How many possible digits can $A$ be?

$$\begin{array}{r}
\mathtt{AOOBAOOB}\\
+\mathtt{BOOABOOA}\\\hline
\mathtt{XXOXYXOXX}
\end{array}$$

$6$
$7$
$8$
$9$
$10$