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. Now, let's consider the sequential insertion of tuples with the following keys into an initially empty B$+$ tree:

$[39,97,38,81,75,-1,41,70,51,67,69,100,91,87,60,52,105,31,10,120]$

I just need clarification on what it is asking, could you explain the question? Here's my understanding:

A block can accommodate a combination of up to $3$ keys: $[($K$1,),($K$2,),($K$3,)].$

Along with $4$ pointers: $[($K$1,$P$1),($K$2,$P$2),($K$3,$P$3),$ P$4],$ where P$4$ is the next pointer.

Each block on the disk has the capacity to hold up to $3$ tuples? What does that sentence mean?

Also what does this mean: 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.

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