题目

                       Mrs. Robinson worked in a big school in America. She had boys and girls in her class, and she always enjoyed teaching them, because they were quick and thought about everything carefully. One day she said to the children, “ People in a lot of countries of Asia wear white clothes at funeral, but people in America  and in Europe wear white clothes when they are happy. What color does a woman wear in this country when she marries?” Mary said , “ White , Miss, because she is happy.” “ That’s good, Mary,” Mrs. Robinson said. “ You’re q化简：（1）2a﹣4b﹣3a+6b（2）（7y﹣5x）﹣2（y+3x）