**Core Concept**
In cases of severe spinal trauma, ensuring the stability of the spine is crucial to prevent further injury and potential neurological damage. This involves immobilizing the patient to maintain spinal alignment and prevent movement, which can exacerbate the injury.

**Why the Correct Answer is Right**
The first step in managing a patient with a spinal fracture and unconsciousness is to immobilize the spine using a cervical collar or a rigid spinal board. This is essential to prevent any movement that could cause further injury to the spinal cord or surrounding structures. The use of a cervical collar or spinal board maintains the alignment of the spine, thereby reducing the risk of exacerbating the injury.

**Why Each Wrong Option is Incorrect**
**Option A:** Administering oxygen is an essential step in managing an unconscious patient, but it is not the first priority in a case of spinal trauma.
**Option B:** Activating the emergency medical services (EMS) is crucial in such cases, but it is not the immediate first step in managing the patient.
**Option C:** Taking vital signs is important in assessing the patient's condition, but it is not the first priority in a case of spinal trauma.

**Clinical Pearl / High-Yield Fact**
In cases of spinal trauma, the patient should be immobilized using a cervical collar or spinal board, and a thorough neurological examination should be performed to assess the level of spinal cord injury. This examination should include assessment of motor function, sensory function, and reflexes.

**Correct Answer:** C. Immobilize the spine using a cervical collar or a rigid spinal board.