题目

单项选择。从A、B、C、D四个选项中选出可以填入空白处的最佳答案 This is such________useful book that I have learned a lot from it.        A. a            B. an            C. the            D. / 答案：A某流程图如图所示，现输入如下四个函数①f（x）=x2②f（x）=1x③f（x）=lnx+2x-6  ④f（x）=ln（x2+1+x）则可以输出的函数的序号是 ．