A, if expressed by the relationship between O2 concentration and CO2 released by respiration, when O2 concentration is low, organisms mainly carry out anaerobic respiration to produce CO2. With the increase of O2 concentration, anaerobic respiration is inhibited, and the amount of CO2 produced is gradually reduced, while aerobic respiration is gradually enhanced, and the intensity of aerobic respiration is also gradually increased, so the amount of CO2 produced by aerobic respiration finally tends to be stable, so A represents the intensity of aerobic respiration and B represents the intensity of anaerobic respiration, so A is correct.

B, for warm-blooded animals, in order to maintain the stability of body temperature at low temperature, the oxygen consumption gradually increases, but after the temperature rises, the oxygen consumption will decrease, which is consistent with curve B, while for warm-blooded animals, the internal temperature is consistent with the external temperature, so the enzyme activity in the body also changes with the external temperature. With the increase of external temperature, the temperature in the body of the temperature-changing animal will also increase, the metabolism will be strengthened, and the oxygen consumption will increase, which is consistent with curve A.

C, the body has just finished eating, the blood sugar concentration in the body is high, and islet B cells need to secrete insulin to reduce the blood sugar concentration. When the blood sugar returns to normal, the secretion of insulin does not increase, and glucagon and insulin are antagonistic, so the curves of the two are opposite, so C is correct;

D. Different organs of plants have different sensitivities to auxin, and roots are more sensitive to auxin, so with the increase of auxin concentration, the growth of roots will be inhibited, which is consistent with curve B, while stems will promote growth, which is consistent with curve A, so D is wrong.

Therefore, choose: d.