I believe it's supporting evidence because it's backing up the main idea of the text, which it's basically supporting your main idea of what you are writing about. hope this helps <3
I say supporting evidence because trivial details are unimportant (that's what trivial means), other main ideas do not help to support each other unless you know that they are related to each other, and the option that the main idea doesn't need support is incorrect. I believe it's incorrect because I was taught that you absolutely needed support to a main idea, meaning the correct answer is supporting evidence. (Hence the word "supporting" because it "supports" the main idea) I hope this helped. :)
