For reasons of safety and ease of maintenance, Washington and dozens of other communities are building rubber sidewalks made【C1】

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问题     For reasons of safety and ease of maintenance, Washington and dozens of other communities are building rubber sidewalks made【C1】______ground-up tires of cars and bikes. The rubber squares are up to three times more expensive than concrete squares but:【C2】______longer, because tree roots and freezing weather won’t crack them. That,【C3】______, could reduce the number of slip-and-fall complaints made【C4】______uneven 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. They【C5】______a way to recycle some of the estimated 290 million tires【C6】______out each year in the United States, and they do not restrict tree roots the way concrete squares【C7】______. Since 2001, a company, Rubber Sidewalks, has been grinding thousands of old tires into small pieces,【C8】______sticky 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【C9】______in two colons 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 residential【C10】______northeast of the capital.
【C7】

选项 A、doing
B、done
C、did
D、do

答案D

解析 本题考查语法结构。本句是个省略句,前文提到restrict,后文为了避免重复,使用动词do来代替restrict tree roots。由于句子是一般现在时,而且concrete squares是复数,所以选D。
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