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

• A

  2mgR

• B

  mgR

• C

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

• D

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