Which of the following are absolute expressions of moisture in the air?

The correct choice is based on the concept of absolute moisture expressions, which help quantify the amount of moisture present in the air without regard to other variables.

Humidity ratio refers to the mass of water vapor present in a specific mass of dry air, making it an absolute measure of moisture. Dew point temperature is the temperature at which air becomes saturated with moisture and water vapor begins to condense, providing a direct indication of the moisture content. Vapor pressure is the pressure exerted by water vapor in the air and is also a measure of the moisture content. All three, therefore, represent absolute moisture content in the air, making them the most appropriate expressions for this context.

In contrast, relative humidity and temperature do not provide absolute values; relative humidity is a percentage that compares the current moisture level to the maximum potential moisture at a given temperature, and while temperature is a crucial factor in understanding air moisture content, it does not quantify moisture itself directly. Humidity ratio and temperature as a combination also do not encapsulate a full absolute measure of moisture like the correct answer does.