The question below consists of a set of labelled sentences. Out of the four options given, select the most logical order of the sentences to form a coherent paragraph.

P. These gases have a profound effect on the earth despite making up only a fraction of all atmospheric gases.

Q. They are a contributor to the phenomenon known as the greenhouse effect.

R. Carbon dioxide, methane, and water vapor are the most important greenhouse gases.

S. Greenhouse gases are gas molecules that absorb infrared radiation and reradiate it back.