B. The sum function is linear but the volume function is not
Step-by-step explanation:
We are given that<u> f(x) and g(x) are linear</u>. Due to this, the sum function S(x) is linear.
And we know the shape of our figure, so we just need to <u>multiply the dimensions</u> for V(x) but <u>the product of three linear functions results in a cubic function, </u>and we conclude V(x) is not linear.