Final answer:
The word 'está' should be used to complete the sentence 'Mi amigo ____ en el gimnasio'. It means 'is' in English and shows the location of the friend at the gym.
Step-by-step explanation:
The correct word to complete the sentence is está. The sentence 'Mi amigo está en el gimnasio' translates to 'My friend is at the gym' in English. The word 'está' is the third person singular form of the verb 'estar', which means 'to be'. In this context, it indicates the location of the friend.
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