What part of the engine ensures that the crankshaft receives power to rotate?

The starter motor is the correct choice because it is responsible for initiating the engine's operation by providing the initial rotation required to crank the engine. When the ignition is turned on, the starter motor engages with the flywheel attached to the crankshaft. This engagement allows the starter motor to turn the crankshaft, enabling the engine to begin its combustion cycle. Once the engine runs, it generates the power needed to keep the crankshaft rotating.

Though the other options are components of the engine or related systems, they do not directly provide power to rotate the crankshaft on startup. The pistons are part of the engine's power generation process but rely on the crankshaft's initial rotation to function. The transmission transmits power from the engine to the wheels but does not provide the initial mechanical energy needed to start the engine. The connecting rod connects the piston to the crankshaft and translates the piston's linear motion into rotational motion of the crankshaft once the engine is already running. Thus, the starter motor is the crucial component for initiating the rotation of the crankshaft.