Which of the following is a correctly written order?

A. ASA gr v q4h prn pain: This order uses outdated terminology ("gr v" for grain 5) and lacks a specified route. Current standards require metric units and a clearly defined route to reduce errors. B. ASA 325 mg po prn fever: While the dosage, route, and indication are present, the frequency is missing. "prn" must be accompanied by a frequency (e.g., q4h) to be a complete and actionable order. C. Aspirin 325 mg po q4h prn headache: This order includes the drug name, dosage, route, frequency, and specific indication. It uses current, safe prescribing standards and is a complete and appropriately written PRN medication order. D. Aspirin po q4h prn toothache: This order is missing the dosage, which is critical for safe medication administration. Without the amount to administer, the order is incomplete and not acceptable for execution.