What are apex test classes?

"Increased test coverage requires large test classes with many lines of code in one method." - I do not agree with that, but answers A and C are incorrect anyway.

Upd: just checked other resources with questions and answers - this question is not multiple-choice.

The only correct answer is D

"Increased test coverage requires large test classes with many lines of code in one method."

If this is true, the developer should be fired.

Code cam and should be extracted to helper methods and even helper classes to keep methods concise and maintainable.