Which is the correct transformation using "not only... but also" for the statements about intelligence and hard work?

The transformation using "not only... but also" is effectively captured in the first choice. This structure emphasizes two positive attributes of the subject, in this case, intelligence and hard work.

By stating "He is not only intelligent but also hard-working," the sentence reinforces the idea that the individual possesses both qualities, creating a parallel emphasis. The structure suggests that these two traits contribute equally to his character.

The other options do not use the "not only... but also" structure correctly. The second option fails to maintain the intended parallelism by splitting the verbs and includes unnecessary wording that complicates the message. The third option lacks the requisite structure to convey the same emphasis, simply stating two independent qualities without the required conjunctions. The final option contradicts the original intent by asserting that he is intelligent while implying a lack of hard work, which diminishes the original dual emphasis present in the first choice.