What does a hydrocarbon emissions test measure?

A hydrocarbon emissions test specifically measures the amount of unburned fuel emissions that are released into the atmosphere during the operation of an engine. This is crucial for assessing the environmental impact of the vehicle and ensuring compliance with regulations aimed at reducing air pollution. Hydrocarbons are a significant component of vehicle emissions that can contribute to smog and other environmental issues, so monitoring their levels helps in understanding how efficiently the engine is burning fuel.

The other choices focus on different aspects of vehicle performance or components. For example, measuring the efficiency of the fuel injection system assesses how well fuel is delivered to the engine, while evaluating a vehicle's overall fuel economy looks at how far a vehicle can travel on a given amount of fuel. Additionally, the condition of the catalytic converter relates to its effectiveness in converting harmful emissions into less harmful substances, but it does not directly measure hydrocarbon emissions. Thus, the core purpose of the hydrocarbon emissions test aligns specifically with option B.