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【单选题】
The biggest threat to the Great Wall is from_____.
A.
humans
B.
erosion
C.
failed restoration efforts
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参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】To protect the Great Wall from weather damage, people______.
A.
take it down
B.
add more stone to it
C.
scrub it
【单选题】Removing salt deposits from rocks makes them more_____.
A.
stable
B.
valuable
C.
likely to erode
【单选题】Both Petra and the Great Wall of Chine are______.
A.
red stone structures
B.
United Nations World Heritage Sites
C.
cities