The correct option is A.
The DNA from one specie differ from the DNA of another specie on the basis of their base ratio. The base ratio refers to the percentage of purine to pyrimidine in a DNA molecule. The base ratio is the one that is responsible for the variability that is observed in chromosomes from different species.
The brain is incorrect. Its the nucleus (the brain is an organ not a organelle)
hope that helps :)
What do you need help with ?
It would be A because textbooks aren't updated for years so he will likely never find it there