Which of the following can be a cause of engine space fires?

Oil line leaks are a significant cause of engine space fires because oil is a highly flammable substance. If there is a leak, the oil can drip onto hot surfaces or electrical components that can ignite it. This risk is compounded by the high temperatures generated in engine spaces, especially during operation. It is crucial for crew members to routinely inspect oil lines and related equipment to ensure the integrity of the system and prevent leaks, thus mitigating the potential for fire.

While gasoline spills can also be a fire hazard, the question specifically identifies oil line leaks as a cause of engine space fires. Faulty brakes tend to relate more to vehicle operation and safety and aren't typically linked to engine space fires. Fuel filter issues could potentially lead to fuel leaks, which may result in fire hazards, but they are not as direct a cause as leaking oil lines.