It has melted. It has sublimated. It has evaporated. It has condensed.
I gave my students this multiple choice question: When moist air comes in contact with a cold surface in the winter, one result can be frost. What has happened to the water vapor in the air to cause frost?

Only one answer is correct among these 4 choices:
- It has melted.
- It has sublimated.
- It has evaporated.
- It has condensed.

Could you tell me which one is correct?

It has sublimated.