If pressure, temperature, and density are all given for understanding layers, which conclusion is most correct?

Correct answer: Pressure and density generally decrease but temperature trend identifies layers

Correct answer: A. In the atmosphere, altitude means greater distance above Earth’s surface. As altitude increases, the column of air above a place becomes smaller, so atmospheric pressure generally falls. Air also becomes thinner, so density generally decreases. Temperature does not follow one single direction through all atmospheric layers: it decreases in the troposphere, increases in the stratosphere, decreases in the mesosphere, and increases in the thermosphere. Therefore, temperature trend is an important clue for identifying layers. B is wrong because pressure does not increase upward and temperature is not always decreasing. C is wrong because the exosphere contains extremely thin gas. D is wrong because temperature is useful for distinguishing layers. Memory cue: pressure and density thin upward; temperature changes direction by layer.