Correct answer:
pusieron
Pusieron is the conjugation of the verb poner for the third person plural in the preterite tense. The preterite tense is one of two simple past tenses. It is used to describe actions that took place or were completed at a certain point in the past. This sentence stands for the third person plural because los viajeros can be replaced by the subject pronoun ellos. Finally:
Los viajeros pusieron la ropa en la maleta.
