Answer: Combustion and Expansion.
Explanation: j took the test!!!
At the step of the four-stroke engine cycle, the heat from the combustion reaction cause the movement of pistons in combustion and expansion, i.e., option A.
An internal-combustion engine goes through four strokes namely intake, compression, combustion, and exhaust which is referred to as four-stroke engine cycle.
When the piston moves during each stroke it leads to the turning the crankshaft.
At the step of the four-stroke engine cycle, the heat from the combustion reaction cause the movement of pistons in combustion and expansion.
Thus, the correct option is A.
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