Which describes the normal boiling point of a substance?
A. The temperature at which the vapor pressure of a substance is greater than the air pressure at sea level.
B. The temperature at which the vapor pressure of a substance is less than the air pressure at sea level.
O C. The temperature at which the vapor pressure of a substance equals the air pressure at sea level.
D. The temperature at which the vapor pressure of a substance equals the air temperature at sea level.