If $\mathrm{r}$ represents the radius of the orbit of a satellite of mass m moving around a planet of mass $\mathrm{M}$, the velocity of the satellite is given by
(A) $\mathrm{U}^{2}=(\mathrm{gM} / \mathrm{r})$
(B) $\mathrm{U}^{2}=[(\mathrm{GMm}) / \mathrm{r}]$
(C) $\mathrm{U}=(\mathrm{GM} / \mathrm{r})$
(D) $\mathrm{U}^{2}=(\mathrm{GM} / \mathrm{r})$