Final answer:
The statement is true; in a crowded room or subway car, the heat level rises due to convection as warmer air rises and cooler air replaces it.
Step-by-step explanation:
The statement that the heat level in a crowded room or subway car rises due to convection is true. Convection is the process where heat is transferred to the air surrounding the skin, causing the warmed air to rise and be replaced by cooler air. This is the same principle that makes a fan make air "feel" cooler by moving air around. Additionally, convection can happen in water, where the body loses heat when the water temperature is lower than the body's temperature, with heat being transferred to cooler water through convection currents.