Read the source given below and answer the questions that follow:
There are six major controls of the climate of any place. They are: latitude, altitude, pressure and wind system, distance from the sea (continentality), ocean currents and relief features.
Due to the curvature of the earth, the amount of solar energy received varies according to latitude. As a result, air temperature generally decreases from the equator towards the poles. As one goes from the surface of the earth to higher altitudes, the atmosphere becomes less dense and temperature decreases. The hills are therefore cooler during summers. The pressure and wind system of any area depend on the latitude and altitude of the place. Thus, it influences the temperature and rainfall pattern. The sea exerts a moderating influence on climate: As the distance from the sea increases, its moderating influence decreases and the people experience extreme weather conditions. This condition is known as continentality (i.e., very hot during summers and very cold during winters). Ocean currents along with onshore winds affect the climate of the coastal areas. For example, any coastal area with warm or cold currents flowing past it, will be warmed or cooled if the winds are onshore.
Finally, relief too plays a major role in determining the climate of a place. High mountains act as barriers for cold or hot winds, they may also cause precipitation if they are high enough and lie in the path of rain bearing winds. The Leeward side of the mountains remains relatively dry.
Q. As one goes from the surface of the earth to higher altitudes, the _________ becomes less dense and temperature decreases.
Correct answer is option 'A'. Can you explain this answer?