Fill in the blank with a suitable adverb from the given alternatives:

The traffic jam was _________ cleared by the traffic police.

Quickly

The correct answer is Option (3) - Quickly

So, the correct sentence is: The traffic jam was quickly cleared by the traffic police.

"Quickly" is the correct adverb to describe how the traffic jam was cleared.

Adverbs modify verbs (in this case, "cleared") to indicate how an action is performed.

"Quick" and "fast" are adjectives, not adverbs, so they do not fit grammatically in this context.
"Fastly" is not a standard adverb form; the correct form is "quickly" for describing the speed of an action.