单项选择题
In the series N1 , N2, N3 , N1=-1, and Nx+1=-1 Nx+x].（）
A. if Quantity A is greater; B. if Quantity B is greater; C. if the two quantities are equal; D. if you cannot determine the relationship based on the given information.
单项选择题 If x+y=16, and if x2-y2=48, then x -y=（）
单项选择题 （）
