The correct answer should be C. parthenon
Parthenon is the famous building that everyone sees on post cards and pictures. It is however located inside the Acropolis. The acropolis is a compound of ancient buildings, and the question asks for only one, so that's why it's the Parthenon.
Only one?
If one then cheerful
If two then gloomy and cheerful
I think Grendel get stuck in a tree because of his careless curiosity of the world above him, that of the humans. He know nothing about that world because he was used to his own world in the underground however he still get tempted to explore. He was also attacked by a bull there because he looks different from the rest of the creatures above.
It surprised people because the dance was much slower and smoother than usual.