Q19

A $B^+$ - tree of order $d$ is a tree in which each internal node has between $d$ and $2 d$ key values. An internal node with $M$ key values has $M + 1$ children. The root (if it is an internal node) has between $1$ and $2d$ key values. The distance of a node from the root is the length of the path from the root to the node. All leaves are at the same distance from the root. The height of the tree is the distance of a leaf from the root.