## **Core Concept**
The question pertains to the implementation and operational aspects of a project or service, likely within a healthcare or similar setting. It involves a series of steps necessary for the successful initiation and functioning of a service or project. The critical step among these is often related to ensuring that the service or project can actually start and function as intended.

## **Why the Correct Answer is Right**
The correct answer, **C. staff trained**, is crucial because without properly trained staff, the equipment ordered and installed, and the service planned and implemented, cannot be effectively utilized. Trained staff are essential for operating equipment, delivering products or services, and ensuring that all aspects of the service meet the required standards. This step directly impacts the quality and safety of the service provided.

## **Why Each Wrong Option is Incorrect**
- **Option A: Service applied** - This seems more like an outcome or a result of several preceding steps rather than a critical step in the process of setting up and initiating a service.
- **Option B: Equipment ordered** - While necessary, ordering equipment is just one part of the process. Without trained staff, the equipment is useless.
- **Option D: Product delivered** - This seems to relate more to the outcome or a specific aspect of the service rather than a critical step in the preparatory phase.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while all the mentioned steps are important in the context of setting up and running a service, the training of staff (**C. staff trained**) is foundational. It directly affects the ability to use equipment effectively, deliver products or services safely and efficiently, and ensure overall quality and patient or client safety.

## **Correct Answer: C. staff trained**