Fill in the blank: Jennings is so ____________ enthusiastic about the game that his enthusiasm spreads to his team-mates.

The most appropriate choice to fill in the blank is "wonderfully." In this context, the blank requires an adverb to modify the adjective "enthusiastic." Adverbs describe or modify verbs, adjectives, or other adverbs, and here it is used to indicate the manner in which Jennings is enthusiastic.

Using "wonderfully," the sentence conveys that Jennings's enthusiasm is characterized by a positive and impressive manner, thus emphasizing the intensity of his enthusiasm.

The other options do not fit the grammatical structure needed for the sentence. "Wonderful" is an adjective, which would not properly modify "enthusiastic." "Wonders" is a noun and does not relate to the sense of enthusiasm being described. "Wondering" functions as a present participle verb, which does not convey the necessary meaning in this context. By choosing "wonderfully," the sentence clearly communicates that Jennings's enthusiasm greatly influences his team-mates.