Using a modulo 26 substitution cipher where the letters A to Z of the
alphabet are given a value of 0 to 25, respectively, encrypt the message
OVERLORD BEGINS. Use the key K =NEW and D =3 where D is the
number of repeating letters representing the key. The encrypted
message is:

A.
BFAEPKEH XRKFAW

B.
BFAEPKEH XRKEAW

C.
BFAERKEH XRKEAW

D.
BFAEQKEH XRKFAW
E. BZAEPKEH XRKFAW
F. BZAEPKEH XRKEAW
G. BZAERKEH XRKEAW
H. BZAEQKEH XRKFAW

Explanation:
The solution is as follows:
OVERLORD becomes 14 21 4 17 11 14 17 3
BEGINS becomes 1 4 6 8 13 18
The key NEW becomes 13 4 22
Adding the key repetitively to OVERLORD BEGINS modulo 26
yields 1 5 0 4 15 10 4 7 23 17 10 4 0 22, which translates to BZAEPKEH
XRKEAW
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