Final answer:
The given sentence 'Juan prefiere esa mantequilla.' is grammatically correct in Spanish.
Step-by-step explanation:
The given sentence Juan prefiere esa mantequilla. is grammatically correct in Spanish.
In this sentence, Juan is the subject, prefiere is the verb, and esa mantequilla is the direct object.
Here, esa mantequilla means 'that butter' in English.
Learn more about Grammar in Spanish