The correct answer to "它是一只猴子的英文怎么写?" is "It is a monkey."
"It" is the subject pronoun used to refer to a non-specific animal or object. In this case, "it" refers to the monkey being mentioned. "Is" is the third-person singular form of the verb "to be" and is used to indicate a state or identity. "A" is an indefinite article used to refer to a single item or animal, in this case, a monkey. And finally, "monkey" is the noun describing the type of animal being referred to.
Therefore, when translated into English, the sentence "它是一只猴子的英文怎么写?" becomes "It is a monkey." This sentence expresses the fact that the subject being discussed is indeed a monkey.