Select the sentence with an error in the adverb used.

Correct option is C

Option (c) contains an error.
Error Explanation: "Thorough" is an adjective; here we need an adverb – thoroughly.
Correct sentence: The students completed the assignment less thoroughly than expected.
Grammar Rule Used:
✔ Adverbs describe how actions are performed and usually end in “-ly”.
Example:
✘ He solved the puzzle quick.
✔ He solved the puzzle quickly.
�� Information Booster:
Adjective → Adverb
careful → carefully
quick → quickly
thorough → thoroughly