A、They are removed for construction. B、They are changed to make the site more interesting. C、They are integrated into the design

I’d like to share with you today my experience with a new approach to building a house. It’s called Envelop Building. Essentially, what it means is that as you are building a house, you try to leave the landscape feature on the land, especially the vegetation, in the original condition. So what you are not doing is the usual practice of land-scraping, by which I mean literally scraping or cleaning the land of any and all the original plants. Why is the approach called Envelop Building? Because instead of clearing everything away, you let your original landscape elements envelop or surround your house. Let the vegetation physical features such as hills and slopes or interesting rock formations, constituted a significant part of the character of the building sight. The design of the house should take these features of the property into account. Actually integrating your original wild landscape with a house is not that new. The famous American architect Wright was doing it about 65 years ago. So we are in good company. Envelop Building is not as easy as it sounds though. It’s not just that you build your house and leave the land alone. By building, you are already damaging the original landscape. But as architects, we should try to work with environment, not against it. A creative architect can find ways to incorporate natural landscape into the overall de?sign. For example, Wright used the massive boulders on the side of one of the most famous houses as part of the house foundation.
Questions 20 to 22 are based on the passage you have just heard.
20. According to the speaker, what does the term "land-scraping" refer to?
21. In Envelop Building, what is done with the landscape features of a building site?
22. Why does the speaker mention the architect Wright?