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: Protists are thought to be the oldest eukaryotes.

Answer: What is thought to be the oldest eukaryotes?


Question: Water and humidity is the critical factor for the survival of segmented worms.

Answer: What is the critical factor for the survival of segmented worms?


Question: Streams often start in mountains.

Answer:
Where do streams often start?