
Solution

1.Nxd6 wins the bishop.
The black rook on e6 is pinned because the rook on e8 is undefended. The variation below illustrates the point:
1.Nxd6 Qxd6 2. Qxd6 Rxd6 3.Rxe8+
1.Nxd6 wins the bishop.
The black rook on e6 is pinned because the rook on e8 is undefended. The variation below illustrates the point:
1.Nxd6 Qxd6 2. Qxd6 Rxd6 3.Rxe8+