10) The radii of three spheres are proportional to 1, 2, 3. Then it follows that:

(A) the volume of the largest sphere is three times the volume of the smallest sphere

(B) the sum of the volumes of the two smallest spheres is equal to the volume of the largest sphere

(C) the volume of the largest sphere is three times the sum of the volumes of the other two

(D) the surface area of the largest sphere is equal to the sum of the surface areas of the other two

(E) the surface area of the largest sphere is three times the sum of the surface areas of the other two.
10) The answer is $(\mathrm{C})$.

The ratio of the volumes of two spheres is equal to the cube of the ratio of their respective radii.

The volumes of the spheres considered are thus proportional to $1,8,27$, so it is easily verified that (C) is true while the others are false (it should be remembered that the ratio of the surfaces of two spheres is equal to the square of the ratio of their respective radii).