What emissions-related parts must be intact to pass inspection?

The correct choice pertains to the essential components involved in controlling vehicle emissions. Catalytic converters, fuel filler caps, and all related hoses play a crucial role in reducing harmful emissions produced by the vehicle's engine.

The catalytic converter is responsible for converting toxic gases produced during combustion into less harmful substances before they exit the vehicle through the exhaust system. If the catalytic converter is missing or malfunctioning, the vehicle would emit higher levels of pollutants, which would not meet regulatory standards.

Fuel filler caps are also critical because they maintain the proper pressure in the fuel system and prevent fuel vapors from escaping into the atmosphere. If a fuel cap is broken or missing, it can lead to evaporative emissions that contribute to air pollution.

Related hoses, such as those connected to the fuel system and the engine, must also be in good condition to ensure that the system operates effectively without leaks. Any malfunction in these hoses could facilitate the escape of harmful vapors.

In contrast, the other choices include parts that, while important for vehicle operation and safety, do not directly impact emissions control or regulatory compliance. Thus, maintaining the integrity of the emissions-related components is vital for passing the Maryland State Inspection.