Answer:
A. The height of a region in relation to sea level
Explanation:
Altitude is the height of a region in relation to sea level, the highest the altitude, the lower the atmospheric pressure, meaning that there will be fewer oxygen molecules and it may cause serious problems to our health. Although most humans live in regions relatively close to the sea level and can not be in regions of 4,900 ft altitudes for long without getting affected, there are certain human populations that have acquired the ability to live normally in high altitudes, such as in the case of people living in Tibet, Asia, people living in the Andes, South America, and those living in Ethiopia, Africa.
