Final answer:
Upon arriving at the scene of a major motor vehicle crash with multiple patients, triage all patients and use your portable radio to call for additional resources.
Step-by-step explanation:
Upon arriving at the scene of a major motor vehicle crash with multiple patients, you should triage all patients first to determine the severity of their injuries. Once the patients have been prioritized, you can use your portable radio to call for additional resources. This will ensure that the most critical patients receive immediate attention and that additional help is on the way.