Final answer:
The basic principle used to regulate vaporizer output is temperature control, which is necessary to maintain constant vapor pressure once equilibrium is reached.
Step-by-step explanation:
The basic principle used to regulate vaporizer output is temperature control. When we consider the properties of gases, it is understood that at a constant pressure, the volume of a gas is directly proportional to its temperature: as temperature increases, volume also increases and vice versa. This relationship is an application of the scientific discoveries of early scientists who noted the direct relationship between gas temperature and volume. When the liquid in a vaporizer is heated, the rate of vaporization increases until equilibrium is reached and the vapor pressure becomes constant. The correct answer to the question is A. Temperature control.