Choose the correct adverb to fill in the blank:

He speaks English ________.

fluently

The correct answer is option (1) fluently

An adverb is needed to describe how he speaks English. "Fluently" is the appropriate adverb here as it describes the manner in which he speaks, indicating that he speaks English with ease and proficiency. Options (2), (3), and (4) are not adverbs and do not appropriately describe the manner of speaking.