How is heat commonly expressed in practical terms?

Heat is commonly expressed in practical terms using various units that relate to its transfer and measurement. British Thermal Units (BTUs) and calories are two well-established units used in everyday scenarios. A BTU is defined as the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit, making it useful in HVAC (heating, ventilation, and air conditioning) applications and in measuring energy content in fuels. On the other hand, a calorie is defined as the amount of heat needed to raise the temperature of one gram of water by one degree Celsius and is often used in dietary contexts to indicate the energy content in food.

In addition, joules, which are part of the International System of Units (SI), also provide a measure of heat energy and are frequently used in scientific calculations. Joules are applicable in various fields and are essential for a comprehensive understanding of thermodynamics.

Thus, the most complete answer encompasses both the British Thermal Unit and the calorie, making it clear why stating "Both B and C" captures the commonly used expressions for heat. The combination reflects a more extensive range of practical applications across fields that rely on measurements of heat.