Which part of speech is not appropriate in formal writing, but often used in daily conversation?

A. Conjunction

B. Preposition

C. Interjection

D. Adverb

The correct answer is C. interjection

Interjections are words loaded with emotion - when you are using them, their meaning is quite clear. For example: Ouch! Yikes! Oh no! Boo!, etc. These are not used in formal writing, whereas it is quite difficult to write a normal sentence without the use of conjunctions (and, or, when, etc), prepositions (in, with, under, etc.), or adverbs (quickly, smoothly, etc.).

The question is asking to choose among the following choices that states the part of speech that is not appropriate in formal writing but often used in daily conversation, base on that the possible answer would be letter C. Interjection. I hope you are satisfied with my answer and feel free to ask for more