Final answer:
The first step in backboarding a standing patient is to manually stabilize the patient's head to prevent further injury to the spine. The correct answer is 3) Manually stabilize the head of the patient.
Step-by-step explanation:
In the technique used to backboard a standing patient, the first step is to manually stabilize the head of the patient. This step is crucial to prevent any additional injury, particularly to the spine, by keeping the head and neck aligned with the spinal column until further immobilization can occur with equipment like a cervical collar or backboard. Once manual stabilization is established, subsequent steps can be safely administered, and this standard procedure is fundamental in emergency medical response and the handling of potential spinal injuries.