Concept:Hard and hardly have different meanings and functions in a sentence.
Explanation:"Hard" can be used as an adjective or an adverb.
As an adjective, it means difficult or tough.
As an adverb, it means with great effort, force, or to a great degree.
For example: "He works hard" means he works with great effort.
"Hardly" is an adverb that means scarcely, barely, or almost not.
For example: "I could hardly hear the sound."
Option B is wrong because "hardly" does not mean very difficult.
Option C is wrong because "hardly" does not mean ever so often.
Option D is wrong because "hardly" does not mean never.
Option A correctly states that "hard" can mean difficult or to a great degree, and "hardly" means scarcely.
Answer:Option A is the correct answer.