Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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Question: Glaciers deposit their sediment when they melt.

Answer: When do glaciers deposit their sediment?

Question: Air quality is a measure of pollutants in the air.

Answer: Air quality is a measure of what in the air?

Question: Many scientists think protists are the oldest eukaryotes.

Answer:
What do many scientists think are the oldest eukaryotes?