To answer this question, let's first be clear about the meaning of the given words.
Agitated means upset, distressed, or unsettled
Anxious means worried, concerned, uneasy, or fearful
Energetic means active, spirited, or tireless
Fretful means distressed, upset, or edgy
Now, let's return to the selection. The narrator is happy, yet, but this happiness is not making him happy. Instead, he describes this happiness as "frightening." It makes him "exhausted" and "paralyzed." He begins pacing back and forth, cracking his knuckles.
Now, if we have to eliminate only ONE word, it could not be either agitated or fretful. First, these two are synonymous, and if we had to eliminate one we would have to eliminate both. Logically, since we cannot eliminate two words, both have to be acceptable. However, he is clearly agitated and fretful based on the narrator's descriptions. He says he is frightened and begins pacing. Thus, both of these words can be used to describe the narrator.
That leaves "anxious" and "energetic." Of these, the man is clearly anxious. Anxious best fits the other words, "agitated" and "fretful." Energetic, however, does not. While energetic means "active" -- and this man is pacing back and forth, making him literally active -- energetic has another layer of meaning. It also means spirited and lively -- enthusiastic.
The narrator, however, describes himself as paralyzed. He is literally pacing but not enthusiastic at all. He cannot work or do anything but ponder this unusual happiness. Therefore, the best answer is C., energetic. This word would not really describe the narrator in this situation.
