用所给词的适当形式填空。 1. At that moment I saw a dog _______(lie) on the floor. 2. At the beginning of the _______(twenty) century,the world's population was 1.7 billion. 3. The _______(shelf) in his study are full of science books. 4. Of all the lessons in Book Three, Lesson Five is the _______(little) interesting. 5. The dog's _______(die) made her very sad. 6. There _______(be) many changes over the years. 7. Who teaches _______(they) physics? 8. How _______(excited) it is to go roller skating here. 9. Most of the students work hard _______(get) high marks in exams. 10. We can live _______(comfortable) in Taizhou because it's a good place.