What can be inferred according to the passage?
选项：

A: The level of oil mist in crankcase can reflect the wear of engine.
B: When oil mist detection equipment is installed, the pressure relief valves may no longer beFitted on crankcase door.
C: Both fuel oil and lube oil mists are monitored by the oil mist detection system.
D: The oil mist detection system functions in the way of releasing the mist out of engine.