The correct answer is C. The troposphere is the lowest layer of Earth’s atmosphere, extending from the surface to an average height of about 12 kilometers (7.5 miles). It is where most of Earth’s weather occurs, as well as where all life on Earth exists. The troposphere is heated from below by the Earth’s surface, and this heat causes the air to rise. As the air rises, it cools and condenses, forming clouds and precipitation. The troposphere is also where the majority of Earth’s water vapor is found.
Option A is incorrect because the troposphere is not a portion of air. The troposphere is a layer of the atmosphere, and the atmosphere is a mixture of gases.
Option B is incorrect because the troposphere is not a portion of water. The troposphere is a layer of the atmosphere, and the atmosphere is a mixture of gases.
Option D is incorrect because the troposphere is not a portion of sky. The sky is the part of the atmosphere that we see above the Earth’s surface, and it is made up of gases, dust, and water vapor. The troposphere is a layer of the atmosphere that is below the sky.