题目内容：

阅读下面短文，在空白处填入1个适当的单词或括号内单词的正确形式

In the 17th century, dentists did their best 1. (make) false teeth. The problem, however, was not making the teeth, 2. was keeping them in place. They had to tie each tooth to the one on either side of it. Only rich people could afford false teeth, 3. were usually made of gold or silver. As more and more people wanted new teeth, poor people 4. (sell)their teeth to the rich so that they could buy food and clothing. During the next 200 years, many changes were made to  false teeth although some of these were not really improvements. Towards the end of the 19th century, for example, cheap elastic teeth were introduced. But they caught fire very 5. (easy), and a number of men were badly burned when their teeth caught fire while they were smoking 6. (cigarette ). Nowadays, false teeth 7. (be) so well made and look so real that it is often 8. (possible)to tell from a person’s appearance whether or not they have them. And in 9. near future, very few people will have them by 10. (add) certain things to the water we drink, we have been able to keep our teeth so healthy that most people will never need false teeth.