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

Processing of filtrate in the proximal tubule helps maintain the ph level in body fluid.
Processing of filtrate in the proximal tubule helps maintain what level in body fluid?

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

The heart does the heartbeat originate in vertebrates.

Where does the heartbeat originate in vertebrates?