①同号两数相乘，符号不变；②异号两数相乘，积取负号；③互为相反数的两数相乘，积一定为负；④两个有理数的积绝对值，等于这两个有理数的绝对值的积．

阅读理解。

    Amy and Sarah are good friends. They are from America. They like winter in America because there are many activities in winter. They can make a snowman,go fishing and go skiing with many friends. There are two festivals (节目) in winter. They're Christmas Day and Thanksgiving. Amy and Sarah are very happy. But they're in Beijing now. They like winter in Beijing, too. Because It's beautiful. It's windy and cold. They're going to visit the Great Wall, so they're very happy.