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

Example Input: Negative growth rate results when birth rates fall even lower than death rates.
Example Output: What results when birth rates fall even lower than death rates?

Example Input: Rubber is an example of a(n) insulators that does not allow electrons to move through them.
Example Output: Rubber is an example of what type of substances that do not allow electrons to move through them?

Example Input: The logistics of carrying out cellular metabolism sets limits on the size of the cell.
Example Output:
The logistics of carrying out cellular metabolism sets limits on what physical property of the cell?