Reading Comprehension
从下列每篇短文的问题后所给的四个选择项中选出一个最佳答案。

     Danger is waiting for you every time you step out of your front door. The hidden danger, however, is not a robber, but merely the sidewalk beneath your feet. Although a short walk down the road may not normally be considered a dangerous activity, a recent government study suggests otherwise.
     Pedestrian's danger tripping up on uneven or damaged sidewalks occurs twice every 100 meters, causing injuries which can match those suffered in a car crash. At least 600,000 trips on sidewalks require medical treatment across the country every year, according to the Pedestrians Association; the government says the figure for serious injuries is a small part of that, though.
     Although the elderly and disabled are the most likely victims of uneven sidewalks, it has caused injuries among thousands of pedestrians of all ages, according to one analyst of the Pedestrians Association's London Office. " Such a fall can sometimes mean a life-changing injury for older people, which leaves them wheelchair-bound or having to walk with a stick, " he said. "A fall can also make people lose confidence, forcing them to stay indoors.”
     According to Pedestrians Association director Ben Mark, the hidden dangers of walking along a sidewalk are not clear by a lack of comprehensive data, concerning the true extent of the problem. He said, “Victims of sidewalk falls are invisible casualties(受伤人员)as far as the National Road Casualty Statistics are concerned—— it only counts if you've been hit by a car or a lorry on the road. It's really bad that we don't know how many people are injured by sidewalks. Nobody keeps track of the data. ”