C). His fond recollections emphasize his genuine sincerity.
Explanation:
As per the question, the narration in the given excerpt influence Oskar's credibility through 'his fond recollections that emphasize his genuine sincerity.' The description of these recollections('hung a pendulum...prove that the earth rotated') reflected that how sincere Oskar was and established his image as a 'genuine and sincere' and emphasize his pure and positive efforts. Therefore, <u>option C</u> best reflects that how the author uplifts Oskar's credibility.
Synonym clue, because a Synonym is a word that is exactly like or nearly like another word, if the word trying to be explained is explained by comparing it to another word is is exactly or nearly like it it is a Synonym Clue.
