Which of the following sentences demonstrates correct grammar and usage?
A.
If any fewer people watch that television series, the affect will be its cancellation.
B.
If any less people watch that television series, the effect will be its cancellation.
C.
If any less people watch that television series, the affect will be its cancellation.
D.
If any fewer people watch that television series, the effect will be its cancellation.

The sentence that demonstrates correct grammar and usage is:
D. If any fewer people watch that television series, the effect will be its cancellation.
Explanation:
Fewer is used with countable nouns (e.g., people), whereas less is used with uncountable nouns.
Effect is the correct noun meaning the result or outcome. Affect is a verb meaning to influence, which is not appropriate in this context.