Water Treatment Filters

What is the role of Carbon filter,sand filter and water softner in RO plant?
According to Nature of ions or substances to be removed by these filters.

Carbon filter contains activated carbon which removes the chlorine content in water and is used to remove the color, odor of the water.
sand filter is used to remove the suspended solids which is present in the water.
Softener is used to reduce the hardness present in water by removing hardness causing ions like magnesium and calcium by using sodium based resins.