Question

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. Which action would have been most likely to keep the snails alive?
A. Adding more plants
B. Adding nitrogen
C. Adding more water
D. Adding another animal species

Answer 1

the answer is A. adding more plants (apex)

Answer 2

Well, the snails probably can't live in water, so what they needed was oxygen. 
well it's not A, not C and not D.
The answer is most likely B