In choosing the best argument in terms of sentence construction and original intention of the author, the following points are considered.
OPTION A - INCORRECT
The mood of the writer does not show a clear meaning between the first and second part of the statement. The use of the conductor "AND" could have been avoided because it means there's no clear meaning as to what the author was referring to.

OPTION B - CORRECT
The use of "BUT" signifies that there's change of course in the argument from the first part before the comma sign which clearly shows that the writer deviated from his initial argument. It's only logical to use the preposition "BUT" here in order to give credibility to the author's credibility.

OPTION C - INCORRECT
The conjunction "ALTHOUGH" means "even though" or "in spite of" which clearly does not fit into the argument here. It means that "in addition to what has been previously said, there are other things which must follow". The second part has only corroborated the first part which isn't clearly what we are looking for.

OPTION D - INCORRECT
We must understand what the conjunction "PR" represents here. I.e. a word used as an alternative to connect two words, phrases, sentences and clauses. "AND" means "in addition to" which means "or" would not be sufficient in replacing "AND" in the sentence because they convey two different meanings.

OPTION E - INCORRECT
This would have been sufficiently correct had it used the pronoun "WHO" instead of the demonstrative pronoun "THAT" in the first appearance of "THAT". Since pronoun are supposed to be replacement words, it's definitely incorrect.