Which of the following best describes the Caesar cipher?

Question $9$Answer

a$.$

Each letter in the plaintext is substituted with a corresponding letter from a Vigen$$re table.

b$.$

Each letter in the plaintext is substituted with a different symbol.

c$.$

None of these

d$.$

The plaintext is transposed according to a fixed pattern.

e$.$

Each letter in the plaintext is shifted by the same number of places down the alphabet.