A code, as is pertains to cryptography:

A.
is a generic term for encryption.

B.
is specific to substitution ciphers.

C.
deals with linguistic units.

D.
is specific to transposition ciphers.

Explanation:
Historically, a code refers to a cryptosystem that deals with linguistic units: words, phrases, sentences, and so
forth. For example, the word “OCELOT” might be the ciphertext for the entire phrase “TURN LEFT 90
DEGREES,” the word “LOLLIPOP” might be the ciphertext for “TURN RIGHT 90 DEGREES”.
Codes are only useful for specialized circumstances where the message to transmit has an already defined
equivalent ciphertext word.
Incorrect Answers:
A: A code is not a generic term for encryption.
B: A code is not specific to substitution ciphers.
D: A code is not a specific to transposition ciphers.

https://www.cs.duke.edu/courses/fall02/cps182s/readings/APPLYC1.pdf