A control apparatus for an internal combustion engine includes an oil pressure regulating valve having a solenoid, a variable cam phase mechanism for changing a cam phase, and an ECU for controlling the oil pressure regulating valve. The transflective pixel structure includes a gate, a gate insulator, a channel layer, a transflective conductive layer, a passivation layer, and a second transflective film. The locks disengage when the housings reach a properly connected state. Following examination of the patient using the stethoscope with the protective head covering, the protective covering can be quickly and easily removed from the stethoscope head and suitably disposed of so as to prevent skin bacteria and like contaminants that may have contaminated the protective cover during patient examination, from undesirably being transmitted to the next patient.