Final answer:
The correct word to complete the sentence is 'slowly,' which is an adverb that modifies the verb 'drive' to suggest how people should operate their vehicles after the storm.
Step-by-step explanation:
The correct word to fill in the blank in the sentence “the meteorologist urged everyone to drive_____after the storm.” is slowly. This is an adverbial form which correctly modifies the verb ‘drive’, indicating the manner in which the driving should be done.
Adverbs are used to describe verbs, adjectives, or other adverbs, and in this case, it tells us how the meteorologist is suggesting people should drive. Using ‘slow’, which is an adjective, would be incorrect because it doesn’t provide information about how to drive, but rather it would improperly describe the noun ‘drive’. ‘Slowest’ is the superlative form of slow, and ‘slowing’ is a verb form; neither are appropriate in this context.