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: In paragraph 2, they had been untouched for centuries does the phrase frozen in time suggest about the figures.

Answer: In paragraph 2, what does the phrase frozen in time suggest about the figures?

Question: Compression zones is the opposite of rarefaction zones, where air molecules in waves are loosely packed.

Answer: What is the opposite of rarefaction zones, where air molecules in waves are loosely packed?

Question: There are four classes of biochemical compounds.

Answer:
How many classes of biochemical compounds are there?