Final answer:
The small end of the connecting rod is attached to the piston by the wrist pin. It is a crucial part of the engine's mechanism to convert linear motion of the piston to rotational motion of the crankshaft.
Step-by-step explanation:
The connecting rod small end is attached to the piston by the wrist pin. The connecting rod is an essential component of an internal combustion engine, which transfers the linear motion of the piston to the rotational motion of the crankshaft. In this scenario, the piston is the correct part that is connected to the small end of the connecting rod via the wrist pin. Other options such as the camshaft, crankshaft, and rod itself are not directly connected to the small end of the connecting rod by the wrist pin.