The sentence from Wonder that best reveals August's feelings through indirect characterization is: "I'm not exaggerating when I say this, but my heart literally started beating like I'd just run the longest race in the world."
This sentence reveals August's intense nervousness and anxiety before meeting Mr. Tushman and the new kids at school. The use of the word "literally" emphasizes the physical reaction he is experiencing, showing how overwhelmed he feels. This sentence provides insight into August's emotional state and his fear of meeting new people, highlighting his vulnerability and sensitivity. By describing his racing heart, the sentence effectively portrays August's anxiety and apprehension in this situation.