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: Unlike ammonia, oxygen cannot be liquefied at room temperature because its critical temperature is below room temperature.

Answer: Unlike ammonia, oxygen cannot be liquefied at room temperature because its what is below room temperature?


Question: Mechanical waves term describes waves that travel through matter.

Answer: What term describes waves that travel through matter?


Question: The length of the sloped surface of a ramp is referred to as input distance.

Answer:
The length of the sloped surface of a ramp is referred to as what?