At its core, RSA is a type of cryptography:

Select one:

a$.$ One$-$time pad, where a unique key is used for each message, rendering it unbreakable.

b$.$ Stream cipher, encrypting the message bit by bit with a keystream.

c$.$ Asymmetric key, where different keys are used for encryption and decryption.

d$.$ Symmetric key, where both parties use the same key for encryption and decryption.