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Dentists always ask questions when it is impossible for you to answer. My dentist had just pulled out one of my teeth and had told me to rest for a while. I tried to say something, but my mouth was full of cotton wool. He knew I collected match boxes and asked me whether my collection was growing. He then asked me how my brother was and whether I liked my new job in London. In answer to these questions I either nodded or made strange noises. Meanwhile, my tongue was busy searching out the hole where the tooth had been. I suddenly felt very worried, but could not say anything. When the dentist at last removed the cotton wool from my mouth, I was able to tell him that he had pulled out the wrong tooth
Dentists always ask questions when it is impossible for you to answer
牙科医生们总是在你无法作出回答的时候向你提出问题。
impossible通常不以人作主语，而以不定式或从句作主语
It is +adj+for/of sb+to do sth
It is+adj+that +句子
如果形容词能够修饰后面的人的性格特征就用of。
对他来说帮助你是不可能的
It is impossible for him to help you. =It is impossible that he will help you.
