The correct answer is option 'B': ha whv. Let's understand why this is the right answer.

Enthalpy of Dry Air (ha):
Enthalpy is the total energy content of a substance and is given by the sum of its internal energy and the product of its pressure and volume. In the case of dry air, the enthalpy is solely dependent on its temperature. Therefore, the enthalpy of dry air can be represented as ha.

Enthalpy of Water Vapor (hv):
Similar to dry air, the enthalpy of water vapor is also dependent on its temperature. However, water vapor has an additional enthalpy due to its phase change. This enthalpy is known as the latent heat of vaporization. Therefore, the enthalpy of water vapor can be represented as hv.

Specific Humidity (w):
Specific humidity is the mass of water vapor present in a unit mass of moist air. It is a measure of the moisture content in the air. Specific humidity is given by the ratio of the mass of water vapor to the sum of the mass of dry air and the mass of water vapor. It can be represented as w.

Enthalpy of Moist Air:
When dry air and water vapor are combined, they form moist air. The enthalpy of moist air is the sum of the enthalpy of dry air and the enthalpy of water vapor. Since the enthalpy of dry air is ha and the enthalpy of water vapor is hv, the enthalpy of moist air can be represented as ha + hv.

However, we need to consider the specific humidity (w) as well. The specific humidity represents the ratio of the mass of water vapor to the sum of the mass of dry air and the mass of water vapor. Therefore, we need to multiply the enthalpy of water vapor (hv) by the specific humidity (w) to account for the mass of water vapor present in the moist air. Hence, the final expression for the enthalpy of moist air is ha + whv.

Therefore, option 'B' (ha whv) is the correct answer.