(D) (ii) and (iv)
Terrestrial plants/animals and consumers like clown fishes/sea urchins are not required. Aquatic plants (producers), herbivorous fishes (consumers), and decomposers (bacteria/fungi) make the aquarium self-sustaining.
Source: Chapter 13, Activity 13.1
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The textbook states that adding aquatic plants and animals makes an aquarium a self-sustaining system. Decomposers (bacteria/fungi) break down dead matter — they are needed. Terrestrial organisms have no role in an aquatic system. Clown fishes and sea urchins are marine/carnivorous consumers not needed when herbivorous fish are already present as consumers. So (ii) terrestrial organisms and (iv) those specific consumers are not required → Option (D).