Final answer:
Vital signs are the part of the 'objective narrative' section of the prehospital care report (PCR) since they provide measurable data of a patient's condition.
Step-by-step explanation:
Of the provided options, the one that is part of the “objective narrative” section of the prehospital care report (PCR) is C. vital signs. The objective narrative of the PCR focuses on factual, measurable data collected by the emergency medical service providers. This would include vital signs, such as blood pressure, pulse rate, respiratory rate, and temperature, as they provide objective measurements of a patient's condition at the scene. In contrast, other options like mechanism of injury, field diagnosis, and chief complaint involve subjective assessments or information provided by the patient which may not be solely based on objective measurements. The objective narrative section of the PCR contains factual information regarding the patient, such as their chief complaint, vital signs, and any diagnoses made by the healthcare provider based on their assessment.