20. The blue whale is the largest animal in the world.

Answer: A

Explanation:

The blue whale is the largest animal in the world in size.

The phrase "the largest animal in the world" correctly uses the preposition "in" to indicate the category or classification of the blue whale, emphasizing its unparalleled size within the animal kingdom.

A) In

This option is correct because "in" appropriately suggests that the blue whale belongs to the category of the largest animals globally. It highlights the whale's status and classification effectively.

B) On

Using "on" would be incorrect in this context, as it typically denotes a surface or a position rather than indicating belonging to a category. Therefore, it does not convey the intended meaning about the blue whale's size.

C) Are

The word "are" does not fit as it is a verb form that implies being or existence, but it does not serve to describe the blue whale's status as the largest animal. It fails to provide the necessary context regarding classification.

D) Been

"Been" is a past participle form that suggests a completed action or state, which is not relevant to the current classification of the blue whale. It does not contribute to the statement about its size, making it an inappropriate choice.

Conclusion

The correct answer, "in," effectively communicates the blue whale's classification as the largest animal in the world. The other options fail to accurately convey this relationship, either by misrepresenting the context or lacking relevance to the classification of the blue whale. Thus, "in" is the only choice that appropriately reflects the meaning intended by the statement.