How many movements of the piston must a four-cycle engine complete before the cycle is complete?

A four-cycle engine, also known as a four-stroke engine, operates through a complete cycle that consists of four distinct strokes or movements of the piston: intake, compression, power, and exhaust.

During the intake stroke, the piston moves down to draw in a mixture of air and fuel. Next, in the compression stroke, the piston moves back up to compress this mixture. The power stroke occurs when the spark plug ignites the compressed fuel-air mixture, forcing the piston down again, thus providing power to the engine. Finally, in the exhaust stroke, the piston moves back up to expel the burnt gases from the combustion chamber.

Therefore, it takes a total of four distinct movements of the piston, each corresponding to one of the strokes, to complete the entire cycle in a four-cycle engine. This is why the correct answer is four.