Which two statements are true regarding B-tree index?

Which two statements are true regarding B-tree index? (Choose two.)

A.
The leaf blocks in the index are doubly linked.

B.
The leaf node stores a bitmap for each key value.

C.
The rows with NULL value in key columns also have entries in the index.

D.
The deletion of a row from the table causes a logical deletion in index leaf block
and the space becomes available for the new leaf entry.