Option A: In $\bf{B^+}$ Tree all leaves are at same level.
In both $B$ Tree and $B^+$ trees, depth (length of root to leaf paths) of all leaf nodes is same. This is made sure by the insertion and deletion operations. In these trees, we do insertions in a way that if we have increase height of tree after insertion, we increase height from the root. This is different from BST where height increases from leaf nodes. Similarly, if we have to decrease height after deletion, we move the root one level down. This is also different from BST which shrinks from the bottom. The above ways of insertion and deletion make sure that depth of every leaf node is same.