The rod and crankshaft convert the up-and-down motion of the piston into

a. a release of exhaust gases.
b. a small, contained explosion.
c. rotary motion.
d. movement in the cylinder head.

answer is c

C. rotary motion.

Explanation:

The rod is a part of the piston that connects it to the crankshaft which refers to several cranks and crankpins where the rods are attached. The rods transfer the energy from the movement of the piston to the crankshaft which generates a rotary motion. When this occurs many times per minute, the engine can move the car.

i think the answer is b.