Topic: Sequence of Tense,

Best Answer Explained in Below-:

The sentence "He found the gold coin as he cleans the floor" uses the phrase "as he cleans," which implies an action happening concurrently with the finding of the coin. Among the provided options, "while cleaning" effectively captures this meaning.

Option D, "while cleaning," indicates that the action of cleaning and the discovery of the coin occur simultaneously, aligning closely with the original sentence's intention. The use of "while" conveys a sense of ongoing action, making it clear that the finding happened during the cleaning process.

On the other hand, option A, "as he had cleaned," suggests a past perfect tense that indicates the cleaning occurred before the finding, which alters the intended meaning. Option B, "while he cleans," awkwardly retains present tense but is less fluid than option D. Finally, option C, "which he is cleaning," introduces ambiguity and changes the focus away from the act of finding the coin.

In summary, "while cleaning" (D) provides a concise and accurate representation of simultaneous actions, aligning perfectly with the original meaning of the sentence.