Basic engine operation can be divided into four stages. These stages (listed in the proper order) are

The answer would be: Intake, Compression, Power, and Exhaust.

Intake: also known as induction or suction.

Compression: starts at the end of the suction stroke, and ends at T. D. C.

Power: also known as combustion. This is the start of the second revolution of the four stroke cycle.

Exhaust: also known as outlet. In here, the piston once again returns from B. D. C. to T. D. C. while the exhaust valve is open. This action eliminates the spent air-fuel mixture through the exhaust valve.