A lightbulb appearing above someone's head meaning “I have a great idea” is because, A) a bright image like a lightbulb is a metaphor of a bright idea, a good and smart idea. ... So when someone has a bright idea, they're having an Edison moment, like Edison's bright idea of the bright lightbulb.
I think it might be vocabulary because you might know the word if you've learned it and its in your vocabulary..? but i don't know..good luck though!!
Indelible means permanent. An indelible moment would be something like going to a job interview and the first impression you make is indelible, it can't be changed or redone.
D. All of the above.
Each of those items are equally important when presenting/preparing.