The correct answer is A.
The atmosphere is divided into five main layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The troposphere is the lowest layer and extends from the surface of the Earth to an average height of about 12 kilometers (7.5 miles). The stratosphere extends from the top of the troposphere to an average height of about 50 kilometers (31 miles). The mesosphere extends from the top of the stratosphere to an average height of about 85 kilometers (53 miles). The thermosphere extends from the top of the mesosphere to an average height of about 600 kilometers (373 miles). The exosphere extends from the top of the thermosphere to an average height of about 10,000 kilometers (6,200 miles).
The troposphere is the layer of the atmosphere that contains most of the Earth’s weather. The stratosphere is the layer of the atmosphere that contains the ozone layer. The mesosphere is the layer of the atmosphere that is coldest. The thermosphere is the layer of the atmosphere that is hottest. The exosphere is the layer of the atmosphere that is closest to space.
The tropopause is the boundary between the troposphere and the stratosphere. The stratopause is the boundary between the stratosphere and the mesosphere. The mesopause is the boundary between the mesosphere and the thermosphere. The thermopause is the boundary between the thermosphere and the exosphere.
The troposphere, stratosphere, mesosphere, thermosphere, and exosphere are all important layers of the atmosphere. Each layer plays a different role in the Earth’s climate and weather.