下列哪个选项中的函数不是所给微分方程的解A. y'' + y = 0, y = 3sin x - 4cos xB. y' = 1 + y^2, y = x^2 + CC. xy' = 2y, y = 5x^2D. y'' - (2)/(x)y' + (2)/(x^2)y = 0, y = C_1x + C_2x^2

A. $y'' + y = 0$, $y = 3\sin x - 4\cos x$

B. $y' = 1 + y^2$, $y = x^2 + C$

C. $xy' = 2y$, $y = 5x^2$

D. $y'' - \frac{2}{x}y' + \frac{2}{x^2}y = 0$, $y = C_1x + C_2x^2$