The central idea is the central, unifying element of the story, which ties together all of the other elements of fiction used by the author to tell the story.
I think that the answer is 10 + 2
I think its an Idiom. I don't see like or as. So no simile. I don't see he is something like a marshmallow. - No metaphor. I also don't see a non-human thing doing human things- the grass was dancing in the wind. My answer would be an idiom.
Hope this helps!
I think it should not Have bad grammar
