a$.$ Which of the following statements is FALSE?

A$.$ Incremental earnings are the amount by which the firm's earnings are expected to change as a result of the investment decision.

B$.$ The average cost of production will generally not change over time.

C$.$ Project externalities in a firm are direct effects of the project that may increase or decrease the profits of other business activities of the firm.

D$.$ Overhead expenses are associated with activities that are not directly attributable to a single project but are usually considered in free cash flow calculations.

This is a past paper question in which the answers haven't been released. I've seen some sites saying its option B$,$ which I agree with. However, I've also seen some sites such as quizlet and a similar multiple choice question on chegg $($didn$\text{'}$t contain option B$)$ that both suggested option C as they explained that project externalities are the indirect effects not direct effect of the project, which I also agree with. I don't know if I$\text{'}$m missinterpreting the wording of option C or not but just looking for some clarification.