Riya checked her answers __________ before handing in the paper.

The correct answer is Option (2) → thoroughly

An adverb is a word that tells how, when, where or how much something happens. It can also describe an adjective or another adverb, for example she sings sweetly, very hot.

Complete sentence: Riya checked her answers thoroughly before handing in the paper. The blank tells how Riya checked her answers. A word that describes a verb (checked) must be an adverb.

Option	What it tells	Example
(1) thorough	an adjective: it describes a noun, not a verb	The doctor gave him a thorough check-up.
(2) thoroughly (answer)	the adverb (thorough + ly): carefully and completely, leaving out nothing	Mother cleaned the kitchen thoroughly before Diwali.
(3) thoroughness	a noun: it names the quality of being careful and complete	The teacher praised the thoroughness of his project.
(4) throughout	in every part of or all through a place or time: it does not tell how she checked her answers	It rained throughout the night.