Two bodies of masses $$m$$ and $$4m$$ are placed at a distance $$r$$. The gravitational potential at a point on the line joining them where the gravitational field is zero is:

A

$$-\dfrac{4Gm}{r}$$

B

$$-\dfrac{6Gm}{r}$$

C

$$-\dfrac{9Gm}{r}$$

D

zero