Final answer:
The correct imperfect tense form of the verb is 'gustaban'
Step-by-step explanation:
The correct imperfect tense form of the verb to complete the sentence is gustaban. The subject of the sentence is 'los instrumentos en el baile', which is plural, so we use the plural form of the verb. In Spanish, when the subject is plural, the verb 'gustar' also needs to be pluralized.
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