Answer:
oxygen
Explanation:
oxygen is an essential nutrient which the body needs especially during respiration.
it help the blood cells do provide energy.
without oxygen, there is no gaseous exchange
<span>Excess nitrogen is brought in the pond from the fertilizer, which are ladden in nitrogen and phosphorous, and rain water or running water takes that nitrogen to the water bodies.Bacteria must have come from the sewage disposal in the pond. Sewage is rich in organic material and allows proliferation of bacteria, which is taken to the pond when the sewage is disposed in the pond.</span><span />
D. is correct: Koalas evolved after trout.
(A is false, B is also false bc amoeba are unicellular, C is false too, they are definitely not in the same class)