instruction:
Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
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:
Mercury is the name of the smallest planet in our solar system, which is also nearest to the sun.
answer:
What is the name of the smallest planet in our solar system, which is also nearest to the sun?

question:
Gravity attracts the earth to the sun.
answer:
What attracts the earth to the sun?