Two charges $$-q$$ and $$-q$$ are placed at points $$(0, d)$$ and $$(0, -d)$$. A charge $$+q$$, free to move along X axis, will oscillate with a force proportional to

A

$$\frac{1}{x^2 + d^2}$$

B

$$\frac{1}{x^2}$$

C

$$\frac{x}{(d^2 + x^2)^{3/2}}$$

D

$$\frac{1}{\sqrt{x^2 + d^2}}$$