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 :

Question

( A ) $-\frac{6 Gm}{r}$
( B ) zero
( C ) $-\frac{9 Gm}{r}$
( D ) $-\frac{4 Gm}{r}$