Here's a problem to solve: 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?

Among the 4 following options, which is the correct answer?

- A: It has melted.
 
- B: It has sublimated.
 
- C: It has evaporated.
 
- D: It has condensed.
 