The DES key size is:

A.
128 bits.

B.
56 bits.

C.
512 bits.

D.
64 bits.

Explanation:
It is 64-bits, but 8 bits are used for parity, so it is 56 bits in effective for the key length. Might be
good to note the clarification (page 703 of CISSP book from Shon Harris – revision 5)