Regarding constructing a good encryption algorithm, what does creating an avalanche effect indicate?

Regarding constructing a good encryption algorithm, what does creating an avalanche effect indicate?

A.
Changing only a few bits of a plain-text message causes the ciphertext to be completely different.

B.
Changing only a few bits of a ciphertext message causes the plain text to be completely different.

C.
Altering the key length causes the plain text to be completely different.

D.
Altering the key length causes the ciphertext to be completely different.

Explanation:
One desirable property of a hash function is the mixing property. What this means is that
a small change in the input (1 bit) should cause a large change in the output (about half of
the bits). This significant change in the outcome is called the avalanche effect.
Example:
The SHA1 function for the first text:
SHA1(“The quick brown fox jumps over the lazy dog”) = 2fd4e1c6 7a2d28fc ed849ee1 bb76e739 1b93eb12
When change “dog” to “log”:
SHA1(“The quick brown fox jumps over the lazy log”)= de9f2c7f d25e1b3a fad3e85a 0bd17d9b 100db4b3
The two results are total different after a little change which is just one “d” to “l”.