The best option to improve the sentence is:
D The names and deeds of some of these men will live in American history, but in the true sense they are unknown because they are misunderstood.
This revision enhances the clarity of the sentence by replacing "and" with "but," which more accurately conveys the contrast between their lasting impact in history and their misunderstanding. Additionally, it makes the phrase "because they are misunderstood" clearer and more grammatically correct.