Which of the following encryption is not based on block cipher?

A.
DES

B.
Blowfish

C.
RC4

D.
AES (Rijndael)

Explanation:
RC4 (also known as ARC4 or ARCFOUR) is the most widely-used software stream cipher and is used in popular protocols such as Secure Sockets Layer (SSL) (to protect Internet traffic) and WEP (to secure wireless networks).