A student creates a model of a closed ecosystem by filling a glass tank half
full with water, then adding 10 snails and two small aquatic plants. The next
day, all the snails are dead. What is the most likely cause of their death?
A. The amount of nitrogen in the tank became too low.
B. The amount of nitrogen in the tank became too high.
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C. The amount of oxygen in the tank became too high.
D. The amount of oxygen in the tank became too low.