A given message and key always produce the same ciphertext.

The following answers are incorrect:

Repetitive encryption obscures any repeated patterns that may have been present in the plaintext. Is incorrect because with Electronic Code Book a given 64 bit block of plaintext always produces the same ciphertext

Individual characters are encoded by combining output from earlier encryption routines with plaintext. This is incorrect because with Electronic Code Book processing 64 bits at a time until the end of the file was reached. This is a characteristic of Cipher Feedback. Cipher Feedback the ciphertext is run through a key-generating device to create the key for the next block of plaintext.

The previous DES output is used as input. Is incorrect because This is incorrect because with Electronic Code Book processing 64 bits at a time until the end of the file was reached . This is a characteristic of Cipher Block Chaining. Cipher Block Chaining uses the output from the previous block to encrypt the next block.