If $$g$$ is the acceleration due to gravity on the earth's surface, the gain in the potential energy of object of mass $$m$$ raised from the surface of the earth to a height equal to the radius $$R$$ of the earth is

A

$$2mgR$$

B

$$\frac{1}{2}mgR$$

C

$$\frac{1}{4}mgR$$

D

$$mgR$$