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 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.

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