C is the answer you are looking for. A common idea isn't a moral, the generalization is the Main Idea, but not quite the moral. The thought of the characters almost never have the moral in them. Therefore, C is your answer.
The foreign translation the definitions
Chugged is the main word that should give it away. It is kind of exaggerating the car going up the mountain. I assume it would be a hyperbole.
Hope I helped!
