The correct option is C That
The correct option is C. The relative pronoun 'that' is used in preference over 'Which' or 'Who', after adjectives in the superlative degree. Hence, Option A and Option B are incorrect. A Pronoun is a word or phrase used in place of a noun. A relative pronoun is a pronoun which is used to refer to a noun (any person, place, thing or idea) that was previously mentioned or heard of. When we use adjectives of superlative degree in a sentence, we should use 'that' to refer to them. An adjective describes the qualities and attributes of a noun. A superlative adjective is used to compare three or more nouns. It takes the comparison of nouns to the highest form. Example: Good, better, best. Best is a superlative adjective. Therefore, when using superlative adjectives in a sentence, we should use 'that' after it. For example: This dress is the best that you can find.