S: Can you tell me what explanations are, please?
L: Well, an explanation involves describing something. Something in general like the eye or a tsunami or a piece of equipment. And then explaining how it works.
S: Oh, so you don't have to choose which the best one is.
L: No, you sort of have to explain how it works, and then describe its significance, say what value it has.
S: Oh, I see. So it's a bit like what you find in a textbook.
L: Yes, very much so. Or an encyclopedia sometimes.
S: OK, thanks.