A knife cutting through food demonstrates the principle of which simple machine?

A wedge is a simple machine with a thin, sloping edge. It turns a push on its thick end into a strong force that splits or cuts through a material.

A knife blade is a wedge. When you press down, the sharp edge forces the food apart.

An axle and a gear help with turning, and a screw is a slope wound round a rod. None of these is the cutting edge of a knife.