Final answer:
The sentence 'Como a una manzana' is grammatically incorrect in Spanish because the preposition 'a' is not necessary in this context.
Step-by-step explanation:
The sentence Como a una manzana is grammatically incorrect as written in Spanish.
The correct form of the sentence should be Como una manzana, which means 'I eat an apple' in English.
The word 'a' is not necessary in this context because in Spanish, the preposition 'a' is usually used to indicate movement towards a person or place, but it is not required when talking about eating or consuming something.
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