The answer is; B
Mutations change the order of nucleotide and therefore affects codons that code for proteins. A different protein is thus produced from the wild type hence creating variations. Genetic shuffling in sexual reproduction, also called gene recombination occurs during meiosis and also when different organisms exchange genetic material such as in bacteria.
I think the correct answer from the choices listed above is the third option. The barrel of a gun is also known as bore. The barrel is the metal tube which the bullet is fired and the bore is the inside of the barrel. It is the one closest to the barrel so it must be the answer.
D would occur more rapidly.
Punnet square
Let's call black 'B' and white 'b'
Being intermediate, gray cats will have the alleles 'Bb'
Being recessive, white cats will have the alleles 'bb'
<u> Gray </u>
|<u> </u>|<u> B | b |</u>
White |b|<u> Bb | bb|</u>
|b|<u> Bb | bb|
</u>
^Apologies for the awful drawing XD
Bb = Gray
bb = White
So the cats can have gray or white fur (A)