Inlet filter of the compressor is chosen by the maximum air flow through it. In other words, the amount of air the compressor sucks in when running at full load.

This should be stated in the specs sheet or manual. It is usallu expressed as Ncfpm (normal cubic feet per minute) or FAD (free air delivery).

So, to answer the multiple choice :) , I would answer "B"

About the air pressure: It is normal for the air pressure to go up and down a little during normal operation.

It's a balance between the compressed air supplied by the compressor and the amount of air used in your factory.

When you use more air than the compressor can supply, the pressure goes down. When you use less air the pressure goes up.

Now, the compressor starts when the pressure reaches the lower pressure setting and stops when the pressure reaches the higher pressure setting.

So, any fluctuation between these two pressures is normal.

If the pressure goes lower, it means your compressor is too small. It can not supply the amount of air that is being used in the factory.

To make it go less up and down (smoother), install a bigger receiver. The bigger the receiver, the more stable the pressure, as you have a larger buffer to pick up large sudden air use.