A man revolves a stone of mass m tied to the end of a string in a vertical circle of radius R. Select the correct pair of the net forces at the lowest and height points of the circle from the given table.

Lowest point	Highest point
(a) ${\mathrm{T}}_1-\mathrm{mg}$	$\mathrm{mg}+{\mathrm{T}}_2$
(b) $\mathrm{mg}+{\mathrm{T}}_1$	$\mathrm{mg}-{\mathrm{T}}_2$
(c) $\mathrm{mg}+{\mathrm{T}}_1-\frac{{\mathrm{mv}}^2}{\mathrm{r}}$	$\mathrm{mg}-{\mathrm{T}}_2+\frac{{\mathrm{mv}}^2}{\mathrm{r}}$
(d) $\mathrm{mg}-{\mathrm{T}}_1-\frac{{\mathrm{m}}_1{\mathrm{v}}_1^2}{\mathrm{R}}$	$\mathrm{mg}+{\mathrm{T}}_2+\frac{{\mathrm{m}}_1{\mathrm{v}}_1^2}{\mathrm{R}}$

Here T₁, T₂ (and v₁, v₂) denote the tension in the string (and the speed of the stone) at the lowest and highest points, respectively.