Which of the Following Is Not True

Which of the following is not true?

A) Mixed costs are comprised of both fixed costs and variable costs, and as a result, mixed costs increase proportionately with an increase in activity level.
B) Mixed costs change in total, but not proportionately with the change in activity level.
C) An electricity bill is an example of mixed costs.The fixed portion represents the cost of having the service available and the variable cost is reflective of actual customer usage.
D) Mixed costs are also known as semi-variable costs.