The radius of a metal sphere at room

The radius of a metal sphere at room temperature T is R, and the coefficient of linear expansion of the metal is α. The sphere is heated a little by a temperature ∆T so that its new Temperature is T + ∆T. The increase in the volume of the sphere is approximately

(a) $2 \pi R \alpha \Delta T$

(b) $\pi R^{2} \alpha \Delta T$

(c) $4 \pi R^{3} \alpha \Delta T / 3$

(d) $4 \pi R^{3} \alpha \Delta T$