Final answer:
The sentence 'Un niño jugaba con los fósforos' uses the Imperfect tense.
Step-by-step explanation:
The verb that uses the Imperfect tense in the given options is Un niño jugaba con los fósforos. The Imperfect tense is used to describe ongoing or continuous actions in the past. In this sentence, the verb 'jugaba' (was playing) indicates a continuous action that was happening in the past.
Learn more about Imperfect tense in Spanish