A particle of mass m is a distance R from the surface of Earth of mass M. The force acting on the particle is F. Which of the following is the gravitational field strength at R?

A. $\frac{{Gm}}{{{R^2}}}$

B. $\frac{{GmM}}{{{R^2}}}$

C. $\frac{F}{m}$

D. $\frac{F}{M}$

C