A、In the lower atmosphere. B、In the upper atmosphere. C、On the Earth. D、Near the Earth. B事实细节题。文章说在离地面50公里处的大气层上层，臭氧层是对人有好处的，因为它

Ozone is a form of oxygen. It is found in the air we breathe and in the upper atmosphere. Near Earth, ozone ii1 the air is a danger to life because it is a pollutant. (33)But between ten and fifty kilometers up in the atmosphere, ozone protects life on Earth. Ozone forms in the atmosphere through the action of radiation from the sun. Ozone blocks harmful radiation from reaching Earth. Scientists say a decrease in ozone and an increase in the harmful radiation will cause many more cases of skin cancer. And it will harm crops, animals and fish.
      (34)Ozone problems first became known in 1985. British scientists reported that ozone levels in the Antarctic atmosphere near the South Pole fell sharply each year in October and November. 1987 was the first year that a huge hole developed in the ozone layer above the Antarctic.
     (35)A recent study of the atmosphere over the Arctic area near the North Pole showed extreme thinning of the ozone. Officials from the American space agency said the latest study is a result of the largest campaign yet to measure ozone amounts and changes in the Arctic area. NASA researcher Paul Newman said some of the measurements show ozone in the Arctic decreased about 60% between January and the middle of March. These measurements are similar to the ozone losses observed in this area a few years ago. (35)Other studies have shown that man-made chemicals were destroying ozone in the atmosphere. An international agreement halted production of the most harmful chemicals. (35)The new findings support the idea that recovery of the ozone layer can not be delayed.