Carbon is moving into the air, and out of the air at the same time. This is because as the tortoise feeds, and inhales O2, the food(cactus-cellulose) is oxidized (glucose + oxygen) during cellular respiration with CO2+H20(waste products)+ATPs( as the main product). The CO2 in the equation is the form by which carbon is liberated into the air.
On a sunny day the Cactus, takes in CO2(with Carbon contents) through the stomata, for photosynthesis. This is the form Carbon enters the cactus at the same time.
A and B are both correct answers, however with the statement of human cloning it does not lead to increased food production through biotechnology, so the only answer would be A
