The school will close **unless** it stops snowing soon. The school will close **until** it stops snowing soon.
Just to be clear, "soon" is a given, and it does not refer to the school closing, it refers to the snow stopping.
I was doing this exercise today with my students, and the only difference between the two sentences is "unless/until". In the exercise, people were supposed to choose between unless/until. According to the answer key, the first answer is correct. I know the second answer is wrong, but what is an easy way to explain to someone that it is wrong? For what reasons?
I have an idea but I need to clarify why the second answer is incorrect. Is it because if I say until, the focus is more on the long state of being closed? “Until”, by definition means up to a point in time. My preference would be to say “The school will be closed until…”. In that situation, we cannot say the school "will close" until. It sounds strange to me.