Final answer:
The sentences 'The rabbit fell down' and 'when I fell off' end with the preposition. Thus, the correct answer is c. Preposition.
Step-by-step explanation:
The sentences "The rabbit fell down" and "when I fell off" end with a preposition. In English grammar, a preposition is a part of speech that introduces a prepositorial phrase and shows the relationship between its object and another element in the sentence. In the sentences provided, the word 'down' and the word 'off' function as prepositions. They are connecting the verbs 'fell' in both cases to additional information about the direction of the action. This directly answers the student's question and confirms that the correct answer is c. Preposition.