题目

In so many ways, cyberspace(网络空间) mirrors the real world. People ask for information, play games, and share hobby tips. Others buy and sell products. Still others look for friendship, or even love.Unlike the real world, however, your knowledge about a person is limited to words on a computer screen. Identity(身份) and appearance mean very little in cyberspace. Rather, a person’s thoughts—or at least the thoughts they type—are what really count. So even the shyest person can become a chat-room star.Usually, this “faceless” communication doesn’t create problems. Identity do一根蜡烛原长a（cm），点燃后燃烧的时间为t（分钟），所剩余的蜡烛的长y(cm)，其中常量是（    ）A.aB.tC.y