Choose the most appropriate option to fill in the blank in the given…

The correct answer is Option (3) → significantly

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: The employees pull up their socks and work significantly harder during appraisals, in the hope of a promotion. Two-step check: 1. part of speech - the blank qualifies the comparative "harder" (the deciding clue), so an adverb. 2. meaning - the adverb must say "a good deal", not "unfairly".

Option	What it tells	Example
(1) apparent	Apparent is an adjective meaning clear or seeming to be true. An adjective cannot qualify "harder" here.	His nervousness was apparent to everyone.
(2) unreasonably	Unreasonably is an adverb, but it means beyond what is fair or sensible. Working hard for a promotion is not unreasonable, so the meaning does not fit.	The shopkeeper charged unreasonably high prices.
(3) significantly (answer)	A word that tells how much more must be an adverb placed before the comparative: much harder, far harder, significantly harder. Significantly means to a large and noticeable degree. During appraisals the employees work a good deal harder than usual, in the hope of a promotion.	Her marks improved significantly after she joined the coaching class.
(4) considerable	Considerable is an adjective (large in amount). The adverb "considerably" would be needed before "harder".	The flood caused considerable damage.