8. Figure P 1.8 shows a frustum of a cone. Of the following mensuration (geometrical) expressions, which describes
(i) the total circumference of the flat circular faces,
(ii) the volume, and (iii) the area of the curved surface?
(a) \pi\left(r_{1}+r_{2}\right)\left[h^{2}+\left(r_{2}-r_{1}\right)^{2}\right]^{1 / 2}
(b) 2 \pi\left(r_{1}+r_{2}\right)
(c) \pi h\left(r_{1}^{2}+r_{1} r_{2}+r_{2}^{2}\right) / 3