TASK DEFINITION: Given scientific fact as input, generate the question from this fact such that it can be answered from the input.
PROBLEM: In machines that increase force, such as ramps and doorknobs and nutcrackers, output is greater is the relation between output and input force.

SOLUTION: In machines that increase force, such as ramps and doorknobs and nutcrackers, what is the relation between output and input force?

PROBLEM: Renewable energy sources emit fewer or no greenhouse gases.

SOLUTION: What type energy sources emit fewer or no greenhouse gases?

PROBLEM: All cells share the characteristic that they need energy.

SOLUTION:
Which characteristic is shared by all cells?