Which of phrases given below each sentence should replace the phrase quotation marks to make the grammatically correct? If the sentence is correct as it is, mark 'D' as the answer.Most of the Indian workers are "as healthy as, if not healthier" than, British workers.

• A. as if healthy as not healthier
• B. healthier but not as healthy
• C. as healthy, if not healthier
• D. No correction required