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

Example Input: Very low density is the concentration of gas molecules in the mesosphere.
Example Output: What is the concentration of gas molecules in the mesosphere?

Example Input: Destructive interference in waves occurs two troughs what things overlap.
Example Output: Destructive interference in waves occurs when what things overlap?

Example Input: Iceland sits on the mid-atlantic ridge.
Example Output:
On which ridge does iceland sit?