Final answer:
August calls Mrs. Garcia's smile "shiny" because he means that her smile is radiant and warm.
Step-by-step explanation:
August calls Mrs. Garcia's smile "shiny" because he means that her smile is radiant and warm (B). In the excerpt, it is described as shining through her thin frame in a sort of glow, which suggests that her smile is bright and positive. Additionally, the use of words like "chilly gold" and "aus-tere glow" in the passage evokes a sense of warmth and brightness, further emphasizing the idea that her smile is radiant.