代入-1得： 1-p+q = -1代入3得：9+3p+q = 3解方程：p = -1，q = -3再看B：f(f(x)) = x => (x^2-x -3)^2 -(x^2-x -3) -3=x=>(x^2-x -3)^2 = x^2=>x^2-x -3 = x 或x^2-x -3 = -x解方程就可以了
