Sentence Correction

In numerous political accounts, the definition most commonly used to describe a strong leader is that of a person who is cognizant of but undeterred by the fluctuations of public opinion.

A. most commonly used to describe a strong leader is that of a person who is cognizant of but
B. that is most commonly used to describe a strong leader is a person who is cognizant of but
C. most commonly used to describe a strong leader is a person who is cognizant but
D. most commonly used to describe a strong leader is a that of a person who is cognizant but
E. that is most commonly used to describe a strong leader is that of person who is cognizant of but also

I'm confused between options A and E. Can any experts help?

The correct answer is Option A because it merges flawlessly into the sentences, completing it perfectly.

Option B is incorrect because the initial words "that is" are superfluous and add nothing to the connection between with the rest of the sentences.
Option C is incorrect because the adjective "cognizant" must be followed by the preposition "of" which is absent in this option
Option D is incorrect because the article "a" used in the phrase "strong leader is A that of..." is incorrect and makes the whole clause grammatically wrong
Option E is also incorrect because of the superfluity of the phrase "that is"