Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

[EX Q]: Water affects the availability of oxygen important element in aquatic environments and in flooded soils.
[EX A]: Water affects the availability of what important element in aquatic environments and in flooded soils?

[EX Q]: Negative growth rate results when birth rates fall even lower than death rates.
[EX A]: What results when birth rates fall even lower than death rates?

[EX Q]: There are about 50,000 vertebrate species, and they are placed in nine different classes.
[EX A]:
There are about 50,000 vertebrate species, and they are placed in how many different classes?