Final answer:
The correct action to take in this scenario is to request clarification from the ordering physician.
Step-by-step explanation:
If a patient arrives with an obvious head trauma, expecting a CT of the brain, but the paper requests a pelvic CT, the correct action to take is to request clarification from the ordering physician. This is important because head trauma may require immediate medical attention, and performing the wrong scan could delay the necessary treatment. It is crucial to communicate with the ordering physician to ensure that the appropriate scan is performed.