Soliloquy happens when a character starts talking to themselves aloud.
Answer:
C. one of the most successful investors in history
Explanation:
The version of the underlined portion of sentence 13 that best accomplishes the goal of convincing the reader to accept the techniques used by Warren Buffet as credible is option C.
This is because, stating that he is one of the most successful inventors in history gives him credibility and authority on the subject.