Therm is the unit of

Answer: Option B

Therm is a unit specifically used to measure a quantity of heat or thermal energy.
Think of it like this:
Power is how fast energy is used (like horsepower in a car).
Heat is the total amount of thermal energy.
Light is a form of electromagnetic radiation.
Distance is how far apart two points are.
So, while power involves energy, a 'therm' directly quantifies the amount of heat.