Which of the following will cause water droplets to condense and fall as rain?

Question

the sun
clouds sweeping into cooler air
lightning
airplanes

Answer 1

Clouds sweeping into cooler air will cause water droplets to condense and fall as rain. When warm, moist air is forced to rise and cools, the water vapor in the air condenses into tiny water droplets or ice crystals forming clouds. As the clouds continue to rise, they get colder and the droplets in them start to combine building bigger drops. Eventually, when the droplets become too heavy to be held up by the rising air currents, they fall to the ground as precipitation, such as rain.