A-gaunt would be your answer
If you look at the excerpt you've been given, he spends the majority of it discussing how he "heard the voice of Merlin from a surprising source." Continuing to read, you see that he heard this through the hooting of the owl outside his window. Using this when we read the question, we can use process of elimination to determine what the best answer is. Each of these answers rings true, but if we use our textual evidence--his discussion of the owl-- we see that the second answer--His inspiration was the owl outside his window--is the best answer for this question. While the other three answers do apply, they are not the best answer since we cannot know how hard he struggled or how long he struggled.
The correct answer is central vision.
