Solipsistic, arresting. Solipsism is literally the theory that only the self exists or can be known to exist (“ solipsistic” is sometimes used a bit figuratively to mean really selfish). Babies could be “sophomoric” (juvenile) or “quixotic” (idealistic or unrealistic), but neither answer choice relates to “unable to be concerned for others, or even to understand a difference between themselves and the world around them.” For the second blank, the “discovery” in question is that “the entire world is not about them.” That’s a pretty earth-shaking discovery for someone who thought otherwise! “Arresting” (striking or dramatic) gets this across. Note the trap answer “selfish,” which is related to the overall meaning of the sentence but does not describe the “discovery.” There is no indication in the sentence that the discovery is “undue” (excessive or unwarranted).