A B$+$ tree can be utilized as a primary index for a relation. Consider a relation R: each block on the disk has the capacity to hold up to $3$ tuples of R; alternatively, a block can accommodate a combination of up to $3$ keys of R along with $4$ pointers, where each pointer refers to a block. It should be noted that in a B$+$ tree, each node is essentially stored in ONE block, and if the B$+$ tree serves as a primary index, the tuples of the relation are stored exclusively in the leaf nodes.