Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
--------
Question: People stopped adding lead to gasoline because of environmental pollution.

Answer: Why did people stop adding lead to gasoline?


Question: Sexual reproduction, in general, relies on sets of cells that are precursors for eggs and sperm.

Answer: What kind of reproduction, in general, relies on sets of cells that are precursors for eggs and sperm?


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

Answer:
Filter feeders called rotifers collect digestive and excretory wastes in what primitive organ?