Final answer:
The correct answer is option B: valve stem, as it is the proper location on a tire to test its pressure for accurate measurement and is based on the principles of tire inflation and pressure changes.
Step-by-step explanation:
The correct answer is option B: valve stem. A technician should test tire pressure at the valve stem, which is the access point for inflating or deflating the tire. This is based on the fundamental principles of how a tire maintains and measures pressure. When air is pumped into a deflated tire, the volume increases with little change in pressure initially. As the tire becomes more inflated, the tire walls resist further expansion, resulting in a rise in pressure as more air is added. When fully inflated, the tire's pressure then increases with temperature changes while driving. It's essential to check the pressure when the tires are cold, as recommended by most manufacturers, making the valve stem the critical point for obtaining an accurate pressure reading.
Checking the pressure at the sidewall, center cap, or tread would not provide an accurate measurement and is not the appropriate method for tire pressure testing. The valve stem is specifically designed for this task and includes a cap that seals the stem to prevent air from escaping.