Which of the following descriptions of data structures is the proper description of a B tree?
a) This structure stores records by finding the physical storage address from a record key value according to a specific algorithm.
b) This structure dynamically re-positions each node in the index in such a way that, considering the key value of this node as middle value, the number of the lower-level records with smaller key values and the number of lower-level records with larger key values are balanced within a given allowance range.
c) This structure associates and stores records using pointers that logically link records independently from their physical location.
d) This structure stores records into access units (pages) such as tracks in the ascending order of the key values, and creates an index that contains the largest key value in each page and the address of this page.