Mount Rushmore needs to be ______.
A、protected from air pollution
B、polished for tourists
C、closed during the winter
D、repaired periodically
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正确答案
试题解析
文章最后一段描述到每年冬天冰雪融水就会流进裂痕,当水结冰时就会膨胀从而使裂痕变得更大,因此每年都会开展维修工作(maintenance work)来填补裂缝。D项为正确答案。periodically定期地,周期性地。