Final answer:
The grammatically correct sentence is 'Luis se afeita la barba.'
Step-by-step explanation:
The grammatically correct sentence is Luis se afeita la barba. In this sentence, 'Luis' is the subject performing the action of shaving ('se afeita') on his own beard ('la barba'). The use of 'la' before 'barba' indicates that the beard being shaved belongs to Luis.
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