Which of these is not an adverb Quickly Big Fast Inadvertently?

The LY forms are obviously adverbs, and FAST can be both an adjective and an adverb. So only the adjective BIG (large) is not an adverb.

* Big is used as an adverb in several colloquial expressions, but this is not formal English. Examples include "Go big or go home" and "Think big." Largely does not mean in a large way, but in a main or predominant way.