题目

化简：11+x+21+x2+41+x4+…+n1+xn-2n1-x2n． 答案：考点：分式的加减法 专题： 分析：在原式中补项是其与第2项合并，进而再和第3项合并，最后得出答案． 解答：解：11+x+21+x2+41+x4+…+n1+xn-2n1-x2n，=-11-x+11-x+11+x+21+x2+41+x4+…+n1+xn-2n1+x2n，=-11-x+1+x(1+x)(1-x)+1-x(1+x)(1-x)+21+x2+41+x4+…+n1+xn-2n1+x2n，=-11-x+1+x+1-x(1+x)(1-x)+21+x2+41+x4+…+n1+xn-2n1+x2n，=-11-x+21-x2+21+x2+41+x4+…+n1+Most of us know we should cut down on fat, but knowing such things isn’t much help when it ________ shopping and eating. A. speaks of     B. refers to    C. comes to     D. focuses on