In this English proverb based sentence improvement question, you must choose the correct form of the well known saying "Old habits die hard" to replace the incorrect sentence "Old habit die hardly".

Introduction / Context:
This question tests knowledge of a common English proverb and the correct use of adverbs and adjectives with the verb "die". The sentence "Old habit die hardly" contains errors in both number and word choice. Examinations frequently use proverbs and fixed expressions because they reveal whether a learner recognises natural set phrases in English.

Given Data / Assumptions:

• Incorrect sentence: Old habit die hardly.
• The intended meaning is that habits which have existed for a long time are difficult to change.
• We must choose an option that matches the standard proverb.
• The correct answer must sound natural and preserve the intended idea.

Concept / Approach:
The standard proverb in English is "Old habits die hard." In this expression, "habits" is plural, matching the generic idea of all habits, and "hard" functions as an adverb meaning "with difficulty". The word "hardly" means "scarcely" or "almost not", which is quite different in meaning and does not fit here. Recognising the fixed proverb helps you quickly identify the correct form in the options given.

Step-by-Step Solution:
Recall the actual proverb used in everyday English: "Old habits die hard."Check the noun: it should be plural "habits" when speaking generally.Check the adverb: "hard" is used to mean "with great difficulty".Reject "hardly" because it means "scarcely" and changes the meaning.Select the option that matches the proverb exactly: "Old habits die hard."

Verification / Alternative check:
When you read "Old habits die hard.", it clearly conveys that changing a long standing habit takes a lot of effort and is not easy. This exact phrase appears in dictionaries of proverbs and in many reading passages. It is therefore the correct standard expression to use in the sentence improvement question.

Why Other Options Are Wrong:
Option A: "Old habits die hardly." uses "hardly" incorrectly. It suggests that old habits almost never die, which is not the established proverb and is grammatically awkward. Option C: "Older habits die too hard." is not a standard idiom and adds "too", which is unnecessary and sounds unnatural. Option D: "No improvement" is wrong because the original sentence has clear grammatical and idiomatic errors.

Common Pitfalls:
Students often confuse "hard" and "hardly". "Hard" can mean "with effort" or "difficult" when used with verbs, while "hardly" usually has the meaning "almost not". In proverb questions, it is also a mistake to modify or partially remember fixed phrases. When in doubt, check if the expression appears in standard reference sources or if you have seen it many times in the same form.

Final Answer:
The correct improved sentence is Old habits die hard.