题目

（理）已知定义域为R的函数，若关于x的方程f2(x)+bf(x)+c=0恰有5个不同的实数解x1,x2,x3,x4,x5,则f(x1+x2+x3+x4+x5)=                                       （  ） A．0                B．2lg2             C．3lg2             D．1 答案：C 解析:.先作f(x)图象，可知f2(x)+bf(x)+c=0两根f1(x)=1且f2(x)≠1.由f(x)图象对称性可得x1+x2+x3+x4+x5=2×5=10，易知选C.California was the first state ________ I had visited in the US．A.whereB.thatC.whichD.what