$[x-(y-z)] - [(x-y) - z] =$
$\textbf{(A)}\ 2y \qquad \textbf{(B)}\ 2z \qquad \textbf{(C)}\ -2y \qquad \textbf{(D)}\ -2z \qquad \textbf{(E)}\ 0$
The expression becomes $(x-y+z)-(x-y-z) = x-y+z-x+y+z = 2z$, which is $\boxed{B}$.