Answer:
The correct option is D. Many a man has tried hard to climb the treacherous mountain range.
Explanation:
Option A is incorrect because it uses the plural verb "were" instead of the singular verb "was" to match the subject "Many a man".
Option B is incorrect because it uses the singular verb "has" instead of the plural verb "have" to match the plural subject "Many men".
Option C is incorrect because it uses the plural noun "men" instead of the singular noun "man" after the phrase "Many a", which should be followed by a singular noun.
Option D is correct because it uses the singular verb "has" to match the singular subject "Many a man".
This sentence correctly combines the singular noun "man" with the singular verb "has" to convey the idea that multiple men have individually attempted to climb the mountain range.
To summarize, the correct option is D. Many a man has tried hard to climb the treacherous mountain range.