Final answer:
According to the fundamental attribution error, the observer would likely underestimate internal factors and assume that the student's stumbling is due to her inherent characteristics like clumsiness.
Step-by-step explanation:
According to the fundamental attribution error, you would explain the student's behavior of stumbling and dropping her books by B. Underestimating Internal Factors and instead overestimating dispositional, or internal, characteristics. This cognitive bias suggests that people disproportionately attribute others' actions to their personality traits rather than to external situational factors. When a person makes an error, like dropping books, an observer influenced by this error would likely think it's due to the person's inherent clumsiness or carelessness, rather than considering situational influences such as slippery floors or the person being off-balance momentarily.