Complete the sentence appropriately: "I found it very ____________ and was feeling quite bored by the end."?

The correct choice is "unexciting" because it is an adjective that directly describes the feeling of boredom experienced in the sentence. The word "unexciting" conveys that the situation lacked interest or stimulation, which correlates with feeling bored. By using this adjective, the sentence effectively communicates that the experience did not capture the speaker's attention, leading to their boredom.

In contrast, "excited" is an adjective indicating a positive feeling and does not fit the context of feeling bored. "Excitation" is a noun that refers to the process of becoming excited but does not work grammatically in the sentence. "Excitement" is also a noun and while it relates to the state of being excited, it does not match the adjective needed to describe how the experience affected the speaker. Thus, "unexciting" is the only word that properly completes the sentence and aligns with the overall sentiment expressed.