The correct answer, "je suis tombé," is the past participle form of the verb "tomber" in the first-person singular form. In French, the past participle is used to form compound tenses, such as the passé composé. In this case, "je suis tombé" translates to "I fell" in English. The verb "tomber" means "to fall," and the past participle agrees in gender and number with the subject, in this case, the first-person singular pronoun "je."