The given sentence has to be filled with the most suitable adverb. Reading the sentence, it is understood that it requires the adverb that means - almost five hours.
Hence, option C is correct. 'It took us nearly five hours to reach the airport', 'nearly' shows the degree of adverb here.
Option A is incorrect, as 'always' means every time. Here, the sentence is about an event that happened once and not every time, hence 'always' is the wrong option.
Option B is incorrect, as 'enough' means adequate or sufficient. 'Sufficient five hours is grammatically incorrect.
Option D is incorrect, as option C is the correct answer.