(b) the number of water bodies in an area
When water bodies are heated during the day, a large amount of water evaporates and goes into the air.
Some amount of water vapour also gets into the atmosphere because of various biological activities.
As the air rises, it expands and cools. This cooling causes the water vapour in the air to condense in the form of tiny droplets.
Once the water droplets are formed, they grow bigger by the condensation of these water droplets. When the drops have grown big and heavy, they fall down in the form of rain.