Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Ex Input:
The main advantage of urea is its very low toxicity.

Ex Output:
The main advantage of urea is its very low what?

Ex Input:
The cardiovascular system in the human body consists of the heart, a network of blood vessels, and blood.

Ex Output:
Which system in the human body consists of the heart, a network of blood vessels, and blood?

Ex Input:
Space is beyond the atmosphere.

Ex Output:
What is beyond the atmosphere?