The correct answer is: A. The length of human hair changes as the relative humidity changes.
Human hair is made up of keratin, a protein that is naturally hygroscopic, meaning it absorbs water from the environment. When the relative humidity is high, the hair absorbs more water and becomes longer. When the relative humidity is low, the hair loses water and becomes shorter. However, the change in hair length is very small and is not usually noticeable.
B. During the winter, low relative humidity can irritate the mucus membranes in the nose and throat. This is because the dry air can cause the mucus membranes to dry out and become irritated. This can lead to symptoms such as a dry cough, sore throat, and nosebleeds.
C. The relative humidity is a measure of the air’s actual water vapor content. Relative humidity is expressed as a percentage, and it tells you how much water vapor is in the air compared to the maximum amount of water vapor that the air can hold at that temperature.
D. A change in the air temperature can change the relative humidity. When the air temperature decreases, the air can hold less water vapor. This means that the relative humidity will increase. When the air temperature increases, the air can hold more water vapor. This means that the relative humidity will decrease.