Which of the following is NOT a part of the exhaust system?

The starter is not a part of the exhaust system. The exhaust system in a vehicle is specifically designed to direct, treat, and expel harmful gases produced by the engine during combustion. Key components of this system include the catalytic converter, which helps reduce toxic emissions; the muffler, which reduces noise from the engine exhaust; and the exhaust manifold, which collects exhaust gases from multiple cylinders and funnels them into a single pipe.

In contrast, the starter is crucial for initiating the engine's operation by turning the engine over and igniting the fuel-air mixture, but it plays no role in managing or expelling exhaust gases. Thus, the correct identification of which component is not part of the exhaust system is the starter.