which of the following best describes how the Vigen$$re cipher works?

a$.$

It transposes the letters of the plaintext in a fixed pattern.

b$.$

None of these

c$.$

It shifts each letter of the plaintext by a fixed number of places.

d$.$

It uses a series of Caesar ciphers based on the letters of a keyword.

e$.$

It substitutes each letter of the plaintext with another letter.