He masses and radii of the earth and moon are M 1 , R 1 and M 2 , R 2 respectively. Their centres are a distance d apart. The minimum speed with which a particle of mass m should be projected from a point midway between the two centres so as to escape to infinity is given by
A 2 [ G(M1+M2)/md ]¹/²
B 2 [ G(M1+M2)/d ]¹/²
C 2 [ G(M1−M2)/md ]¹/²
D 2 [ G(M1−M2)/d ]¹/²