Because all enzymes are specific in nature therefore the must fit to their specific substrates so if the shape is changed it might not fit perfectly to it's substrate.
It causes the introduction of new genes to the existing gene pool creating a variation, so that the best one is selected by the nature.
The answer is A. The heart pumps blood through the circulatory system, and the lungs help the oxygen transport throughout the respiratory system. :)
I think this is ether b. Trait or C. Allele, pretty sure it’s allele though. Good luck!