题目内容：
请根据以下内容回答题：Directions: There are 10 blanks in fhe following passage. For each numbered blank,there are 4 choices marked A, B, C and D. Choose one to complete the dialogue and mark your answer on the ANSWER SHEET with a single line through the center.For reasons of safety and ease of maintenance, Washington and dozens of other communities are building rubber sidewalks made 76 ground-up tires of cars and bikes. The rubber squares are up to three times more expensive than concrete squares but 77 longer, because tree roots and freezing weather won't crack them. That, 78 , could reduce the number of slip-and-fall complaints made79uneven pavements. The shock absorbing surface also happens to be easier on the joints of slow runners and more forgiving when someone slips or falls, and the rubber sidewalks are considered more environmentally friendly. They80 a way to recycle some of the estimated 290 million tires 81out each year in the United States, and they do not restrict tree.roots the way concrete squares82 . Since 2001, a company, Rubber sidewalks, has been grinding thousands of old tires into small pieces,83sticky substances and baking the material into sidewalk sections that weigh less than eleven pounds a square foot, or a quarter of the weight of concrete. The rubber squares are now 84 in two colors of gray and orange. The District of Columbia has spent about $60,000 to replace broken concrete with the rubber squares here and there in a residential85northeast of the Capital. A．by
B．on
C．of
D．for
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