Here are the correct answers for the text:

19. B. **production**
20. C. **sustainable**
21. A. **tried**
22. B. **got**
23. C. **end**
24. C. **harm**

So the filled text would read as follows:

"Fast fashion is the mass **production** (19) of clothes at a low cost. They are put in shops and online quickly to create high demand. Every year, manufacturers make 100 billion clothes, and this is expected to grow by 60 by 2030. Sadly, this way of making and selling clothes is not very **sustainable** (20). Many years ago, people went to stores and **tried** (21) clothes on. They took more time and thought more carefully before buying. The clothes were also of better quality, so people wore them for a longer time. Today, people order cheap clothes on the Internet, and if they don’t like them, they send them back. **Some** (22) people buy clothes and never even wear them. Many of these are often of poor quality to recycle; people don’t want to buy them second-hand. So huge quantities **end** (23) up in landfills, causing great **harm** (24) to the environment."