Parts of the following sentence are given as options. Identify the segment that contains a grammatical error.
Both are excellent singers, but I think Kartik is best.

Correct option is D

The segment that contains a grammatical error is is best.
Since the sentence compares two singers, "Kartik" and "another singer," the correct form would be "better" instead of "best," which is used for comparisons involving three or more entities.
Grammatical Rule Used: When comparing two entities, the comparative form of the adjective should be used, not the superlative.
Corrected Sentence: Both are excellent singers, but I think Kartik is better.
Example:
· She is the smarter of the two. This correctly uses the comparative form "smarter" when comparing two people.