题目

请听材料，回答问题。 （1） What does the man help Mrs. Brown do? A . Baby-sit for her. B . Clean the house. C . Look after her mother. （2） What does the man want to do? A . Buy a birthday present. B . Buy a Mother's Day present. C . Buy a Women's Day present. 答案：A B对于函数f(x)=x-1x+1，设f2(x)=f[f(x)]，f3(x)=f[f2(x)]，…，fn+1(x)=f[fn(x)]（n∈N*，且n≥2），令集合M={x|f2007（x）=x，x∈R}，则集合M=______．