During the Four-Stroke Cycle, Which Event Is LEAST-Likely to Occur

During the four-stroke cycle, which event is LEAST-Likely to occur during the power stroke?

A) The piston moves back up, forcing any remaining exhaust gas from the cylinder through the open exhaust valve.
B) The burning fuel expands rapidly.
C) The piston moves back down in the cylinder.
D) The exhaust valve opens as the piston approaches the bottom of its travel.