解析：选D　细节理解题。根据Machu Picchu部分中的"The forces of natural erosion have been accelerated by tourism and this landmark faces severe influence from increasing foot traffic."可知，旅游业给该地带来了破坏，即带来了沉重的生存负担。故选D。

　　22．Which place probably needs visitors to dive into the water to enjoy its beauty?

　　A．Venice.

　　B．Machu Picchu.

　　C．Glacier National Park.

　　D．The Great Barrier Reef.

　　解析：选D　细节理解题。根据The Great Barrier Reef部分中的"Hidden from view beneath the waves"可知，该地可能需要游客潜入水中才能享受其美景。故选D。

　　23．What do the above attractions have in common?

　　A．They all have a long history.

　　B．They're all threatened by climate change.

　　C．They're all in danger of disappearing.

　　D．They're all well­known for natural scenery.

　　解析：选C　推理判断题。根据Venice部分中的"this city will disappear back into the water at an even faster rate"， Machu Picchu部分中的"the future of Machu Picchu remains uncertain"， Glacier National Park部分中的"the glaciers that are part of the beauty of this national landmark will disappear entirely in the next two decades"及The Great Barrier Reef部分中的"the Great Barrier Reef has been rapidly dying off"可推知，这几处旅游胜地的共同点是它们都濒临消失。文章第一段的内容也是暗示，故选C。

　　B

　　(2018·吉林公主岭市三中模拟)People say dogs are our best friends. Sometimes, they are our saviours (救星)．

　　In 1925, the town of Nome in Alaska was struck by diphtheria, a disease that can be passed easily from one person to another. Left untreated, it can prove fatal.

The outbreak had come at the worst time. Nome was cut off by the worst winter in 20 years and there was no local stock of medicine to prevent the spread of the disease. Moreover, the closest supply was 674 miles away, in Nenana. On January 24, 1925, Nome's Board of Health voted to use a dogsled (狗拉雪橇) relay to transport the medicine from Nenana to Nome. 20 dogsled teams positioned themselves along the route. Leonhard Seppala was set to make the last but two leg from Shaktoolik to Golovin.