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

Q: Filter feeders called rotifers collect digestive and excretory wastes in cloacal bladder primitive organ.

A: Filter feeders called rotifers collect digestive and excretory wastes in what primitive organ?
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Q: Multiple genes mutations is usually necessary to develop cancer.

A: What is usually necessary to develop cancer?
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Q: A wall of rocks or concrete a called a groin.

A:
What is a wall of rocks or concrete called?
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