Answer =B.
This case of deletion will come when node will have both left and right child.
So in order successor will come from right subtree tree.
In order successor will be left most child from right subtree.
So there can be two cases:-
1. The right subtree root will have left child. In that case we get successor from leftmost child
2. The root of right subtree(of the node to be deleted) has empty left tree. In that case root of right subtree will become the successor.