题目

     One day, a poor boy who was trying to pay his way through school by selling goods door to door found that he only had one dime （=10 cents） left．He was hungry, so he decided to beg for a meal at the next house．      However, he lost his nerve when a lovely young woman opened the door．Instead of a meal he asked for a drink of water．She thought he looked hungry, so she brought him a large glass of milk．He asked, How much do I owe you?      You don't owe me anything, she replied．Mother has taught me never to accept pay for a kindness． He said, Thank y8．已知y=（k-1）x${\;}^{{k}^{2}+k-1}$是正比例函数，则k=-2．