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

[EX Q]: Filter feeders called rotifers collect digestive and excretory wastes in cloacal bladder primitive organ.
[EX A]: Filter feeders called rotifers collect digestive and excretory wastes in what primitive organ?

[EX Q]: Exotic species are also called invasive species because they threaten other species.
[EX A]: Why are exotic species also called invasive species?

[EX Q]: Many species of birds in new england fly south for the winter months to find an environment with more food.
[EX A]:
Which of the following best explains why many species of birds in New England fly south for the winter months?