A semi-variable cost: A. Increases and decreases directly and proportionately with changes in volume.
B. Changes in response to a change in volume, but not proportionately.
C. Increases if volume increases, but remains constant if volume decreases.
D. Changes inversely in response to a change in volume.

B. Changes in response to a change in volume, but not proportionately.

Explanation:

A semi variable cost (or mixed cost) is a cost or expense that is partially fixed (does not change according to production output) and is also partially variable (changes according to production output). An example of semi variable costs are utilities which have a fixed minimum level per month and they increase as production output increases. Another example is the cost of a car, where insurance and lease payments are fixed but gas and maintenance expenses vary according to the number of miles driven.

answer; i believe the correct answer is radioactive decay);

answer utilities; more money you have to pay out ; )