The correct answer is B) Pressure-Demand Self-Contained Breathing Apparatus (SCBA). In a hydrogen sulfide (H2S) environment on a MODU, a pressure-demand SCBA is the preferred respiratory protection for repair/investigation personnel. This is because pressure-demand SCBAs provide a positive pressure within the facepiece, ensuring that any leaks will force clean air outward rather than allowing contaminated air to enter. This offers superior protection compared to other SCBA types or emergency escape devices in a hazardous H2S environment. The other options, while potentially suitable for other applications, are not as well-suited for the specific hazards of an H2S environment on a MODU. For example, demand SCBAs (choice D) do not maintain positive pressure, and emergency escape devices (choice A) are intended for short-duration, rapid exits rather than prolonged work in a hazardous atmosphere.