The potential energy of a particle of mass m in a conservative force field can be expressed as
$$U = \alpha x - \beta y$$ where (x, y) denote the position coordinates of the body. The acceleration of the body is

A

$$\frac{\alpha - \beta}{m}$$

B

$$\frac{\alpha + \beta}{m}$$

C

$$\frac{\sqrt{\alpha^2 - \beta^2}}{m}$$

D

$$\frac{\sqrt{\alpha^2 + \beta^2}}{m}$$