Given two sequences $X$ and $Y$:
$X=\langle a, b, c, b, d, a, b \rangle$
$Y=\langle b, d, c, a, b, a \rangle$
The longest common subsequence of X and Y is:
- $\langle b, c, a \rangle$
- $\langle c, a, b \rangle$
- $\langle b, c, a, a \rangle$
- $\langle b, c, b, a \rangle$