Which of the following would best describe a Concealment cipher?

Which of the following would best describe a Concealment cipher?

A.
Permutation is used, meaning that letters are scrambled

B.
Every X number of words within a text, is a part of the real message

C.
Replaces bits, characters, or blocks of characters with different bits, characters, or blocks.

D.
Hiding data in another message so that the very existence of the data is concealed.

Explanation:
Reference: pg 468 Shon Harris: All-in-One CISSP Certification