题目

设x，y满足约束条件，若目标函数z=ax+by（a＞0，b＞0）的最小值2，则ab的最大值为（ ）A． 1       B．        C．         D． 答案：C．John once told me a story about his friend, Michael. Michael happened to be on a train sitting next to a young man who seemed worried. Finally the young man told the friend that he was a convict (罪犯) returning home from a prison far away. What he did had brought shame (羞耻) on his family, and they had neither visited him nor written to him. He hoped, however, that this was only because they were too poor to travel and too busy to write. When he was set free he had written to tell them he wanted to go home. To make matters easy for them, however, he had asked them to put up a signal (信号) for him when the train passed their little farm. If the family had forgiven (原谅) him, they were to put up a white ribbon (丝带) in the big apple tree near the railway. If they didn't want him back, they were to do nothing, and he would stay on the train, and go far away. As the train neared his hometown his suspense became so great that he was afraid to look out of the window. He asked Michael to watch for the big apple tree. They changed seats. In a minute, Michael put his hand on the young convict’s shoulder, "There it is," His eyes was filled with sudden tears. "It’s all right. The whole tree is white with ribbons."1.According to the passage, the white ribbon in the big apple tree means ________.A.pleasureB.forgiveness(原谅）C.happinessD.education2.The word "suspense" underlined in the last paragraph can best be replaced by ________.A.angerB.interestC.worryD.happiness3.Why was Michael asked to watch for the apple tree?A.The young man was afraid that he was refused by his family.B.The young man’s seat was far from the window.C.The young man was afraid of seeing the white ribbons in the tree.D.The young man was sure that his family would accept him.4.Why did Michael cry at the end of the story?A.The young man couldn’t live with his family.B.There were many white ribbons on the apple tree.C.He was afraid.D.The young man was very sad.