四、语法填空。 阅读下面短文，在空白处填写1个适当的单词或括号内所给单词的正确形式。 There is a small thing we use every day. We usually put it in the bathroom. Without it, we might have tooth 1.______ (problem). Can you guess what it is? Yes, it's the toothbrush. But do you know anything about 2.______ (it) history? According to some research, before toothbrushes appeared, the ancient Chinese people used some small tree branches (树枝) 3.______ (clean) their teeth. About 800 years ago, people made a kind of brushes with pig hair and bamboo. It might be 4.______ (early) form of toothbrushes in the world. As time went by, the forms of toothbrushes changed. For example, people 5.______ (choose) horse-tail hair instead of pig hair 6.______ pig hair was too hard. Imagine that you travel back to hundreds of years ago and brush your teeth 7.______ (comfortable). It sounds fantastic, doesn't it? In 8.______ 15th century, the Chinese toothbrush found its way into Europe. It became popular among local people soon. The 9.______ (invent) of toothbrushes was not as famous as that of paper-making, but it was very 10.______ (use) in our daily life. Today we have a good habit of brushing teeth. We should thank the ancient Chinese for it.