How would an unexpected result to an experiment affect the original hypothesis

The best answer here is sentimental because the quotes used recall a time in the past of the speaker, one that he obviously thinks of fondly. If we look at the other choices, we can see that they don't make much sense because there is nothing about the passage that is judgmental, solemn, or brave. But, since he is recounting his adventures in the woods and the library, even stating that it was all an adventure, sentimental makes the most sense.