Read the excerpt about ozone from a nasa publication. "ozone is a gas . . [that] occurs naturally in small (trace) amounts in the upper atmosphere. . ozone protects life on earth from the sun's ultraviolet (uv) radiation. . near the earth's surface, ozone is created by chemical reactions between air pollutants from vehicle exhaust, gasoline vapors, and other emissions. at ground level, high concentrations of ozone are toxic to people and plants." —nasa ozone hole watch which statement best summarizes the main idea being expressed?