I think the answer is D. A good indicator is the resting heart rate. Exercise strengthen your heart and it makes it more efficient. The resting heart rate shows of the heart is pumping blood normally each time it contracts. Having a normal resting heart rate would mean a healthy heart.
They are distinguished by proteins on the erythrocytes.
The organism would be a secondary consumer and a carnivore. An example could be an snake in the following food chain: grass -> bunny -> snake
64 triples of nucleotides