1. The problem asks: What is the purpose of a tire pressure gauge? 2. A tire pressure gauge is a tool used to measure the air pressure inside a tire. 3. This is important because maintaining the correct tire pressure ensures safety, improves fuel efficiency, and extends tire life. 4. The options given are: A. Measure wheel alignment B. Measure tire tread depth C. Measure tire air pressure D. Measure wheel balance 5. Among these, the correct purpose of a tire pressure gauge is to measure tire air pressure. 6. Therefore, the correct answer is **C. Measure tire air pressure**.