My answer is
(C). It took me 45 seconds.
Because all options start with "The", this question should not have underlined the complete sentence. The minor distinction matters: when the full sentence is underlined, we should instinctively start by locating a sentence structure that is efficient and logical.
(A) Passive voice is not as effective as positive one.
Especially in comparison with (C), it is also not concise or efficient.
(B) See above.
(C) correctly uses "Comma + present participle phrase" to show the effect of the previous clause.
(D) Adverb "condescendingly" modifies adjective "self-righteous" when its adjective form "condescending" should be used to modify "manner".
(E) "having alienated" means that after "having alienated many senators", the lobbyist started to behave "condescendingly and self-righteously" probably because the lobbyist realized that feigned deference posture did not work to befriend those snobbish senators who can only be swayed by monetary incentives.
Now, that interpretation might actually be the case, and this version cannot hence be deemed wrong in itself.
Change "the lobbyist” to "the U.S. President", and this sentence sounds even better.
Still, it is eliminated because it confuses the chronology.