You are presented with the quiz "What about the temperature may cause water vapor to condense overnight and in the early morning?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "dew is formed when water vapor condenses over night" and "dew point is the temperature at which dew forms". 

So, what's the best answer to the question?


 

 It reaches the dew point          