A、The rebuilt part of the wall. B、The wind-beaten valleys. C、The disappearing rock face. D、The overgrowing plant life. D短文提到，作者爬

Climbing the Great Wall must have been thirsty work. It was lucky for the climbers all those years a-go that they could buy ice water from people along the way. If it got cold, they could always buy an "I climbed the Great Wall" T-shirt and perhaps even go to KFC for dinner. OK, maybe this isn’t quite true. But it does make a very important point: some parts of the Great Wall have been reduced to marketplaces. Sections of the Wall close to Beijing are now full of tourists, with salespeople standing around the gate. As a result, it loses all sense of history. With this in mind, last weekend I went to the "Wild Wall", where the salespeople do not come. Here the Wall is overgrown with plant life. Trees stick out between the stones. In some steeper places, the steps have completely disappeared and you have to climb the rock face, pulling your body up with your arms if you can’t find a place to put your feet. It is amazing to see the Wall climb hills before diving into valleys. There are beautiful watchtowers standing on cliff tops where they are beaten by the wind. But perhaps the most striking thing of all is how natural it all looks. This Wall hasn’t been rebuilt to look like new; it has aged with the land around it over hundreds of years. Watching the sun rise above the branches of trees whose roots stretch deep into the heart of the Wall, you feel you are standing on a man-made structure that has indeed become part of nature.
19. What has the Great Wall lost according to the speaker?
20. Which scene did the speaker enjoy on the "Wild Wall?
21. What is the most striking thing about the "Wild Wall"?