Which of the following algorithms has the SMALLEST key size?

Correct answer is: A) DES

Twofish is a new block cipher with a 128 bit block, and a key length of 128, 192, or 256 bits, which has been submitted as an AES candidate.

DES is a block cipher that operates on data blocks of 64 bits in size. DES uses a 64-bit key 8 × 8 including 1 bit for parity, so the actual key is 56 bits. DES, in common with other block ciphers, is based around a structure called a Feistel Lattice so it is useful to describe how this works.