Air currents move water vapor around the globe, and when these currents reach a certain point of saturation, the water vapor condenses and forms cloud particles. These cloud particles then collide with each other, causing them to grow in size. Eventually, these particles become too heavy to be supported by the air currents and they fall out of the sky as precipitation, which can take the form of rain, snow, sleet, or hail. Therefore, precipitation is the correct answer.