Hi, there your answer is A. Sea bueno
Hope this helps :)
a) Sea bueno
Disclaimer: I'm in Spanish 2. I am not a native Spanish speaker. I've answered the question to the best of my ability and double-checked on Spanishdict so I believe I am correct but I'm not the best source.
The Oak Tree
The Oak Tree uses an external energy force, but does not require any work from ones self.