The capitalized word is the one that the missing adverb modifies. Fill in all the gaps with any word that makes sense, and then press "Check" to check your answers. If what you wrote is what we might expect, that word will be an adverb. There may be many other adverbs that would fit, of course, far too many to be anticipated in making the answer key, so limit yourself to the boring old norm, please.
Adverbs are words that modify verbs, adjectives, or other adverbs. Like adjectives, many adverbs can be compared in degree although rather few can actually take the -er and -est endings. We do sometimes hear oftener and oftenest, but most adverbs admitting of degree take more, most, less, and least (or, for concepts better measured by number, fewer and fewest):
She was less shabbily dressed than usual.
Although a large class of adverbs end in -ly (adverbs of manner), some adjectives also end in -ly (e.g., homely, lovely, manly, etc.), and there are adverbs which do not end in -ly (sometimes, for example). The only sure way of telling an adjective from an adverb is to find what it modifies. In the sentences in the right window, the words modified by the missing adverb are capitalized.