The following text is for questions 1 to 5.

    Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. It is the primary connection in the water cycle that provides for the delivery of atmospheric water to the Earth. Most precipitation falls as rain.

    The clouds floating overhead contain water vapour and cloud droplets, which are small drops of condensed water. These droplets are far too small to fall as precipitation, but they are large enough to form visible clouds. Water is continually evaporating and condensing in the sky. If you look closely at a cloud you can see some parts disappearing (evaporating) while other parts are growing (condensation). Most of the condensed water in clouds does not fall as precipitation because their downward speed is not large enough to overcome updrafts which support the clouds. For precipitation to happen, first, tiny water droplets must condense on even tinier dust, salt, or smoke particles, which act as a nucleus. Water droplets may grow as a result of additional condensation of water vapour when the particles collide. If enough collisions occur to produce a droplet with a downward velocity which exceeds the cloud updraft speed, then it will fall out of the cloud as precipitation. This is not a trivial process, since millions of cloud droplets are required to produce a single rain drop. A more efficient mechanism (known as the Bergeron-Findeisen process) for producing a precipitation-sized drop is through a process which leads to the rapid growth of ice crystals at the expense of the water vapour present in a cloud. These crystals may fall as snow, or melt and fall as rain.

(Source: https://water.usgs.gov/edu/watercycleprecipitation.html)

What is the main idea of the second paragraph?