题目

Sales of CDs have greatly increased since the early 1990s, when people_____ to enjoy the advantages of this new technology.    A. begin              B. began           C. have begun         D. had begun   答案：B.下列表格是二次函数的自变量x与函数值y的对应值： … -3 -2 0 1 3 5 … … 7 0 -8 -9 -5 7 … 则二次函数中当x=2时，y=_________