An Atmospheric Scientist Would Like to Explain the Concept of Dew

An atmospheric scientist would like to explain the concept of dew point to someone who is unfamiliar with the concept. They could best illustrate this atmospheric characteristic by explaining that dew point is the

A) same as relative humidity.
B) highest temperature to which air can be heated at a constant pressure before liquid droplets will appear.
C) lowest temperature to which air can be cooled at a constant pressure before the air becomes dry.
D) lowest temperature to which air can be cooled at a constant pressure before liquid droplets will appear.