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Lesson23 A new house 新居
I had a letter from my sister yesterday.She lives in Nigeria.In her letter,she said that she would come to England next year.If she comes,she will get a surprise.We are now living in a beautiful new house in the country.Work on it had begun before my sister left.The house was completed five months ago.In my letter,I told her that she could stay with us.The house has many large rooms and there is a lovely garden.It is a very modern house,so it looks strange to some people.It must be the only modern house in the district.
请分析In my letter,I told her that she could stay with us.（还有为何用could）
请详细分析（不是翻译），从时态，结构，that，could分析