Which of the following would make the best topic sentence for a paragraph about fresh water swamps?
a- Freshwater swamps play a very important role in not only balancing the natural ecosystem, but also protecting human development from the elements
b- In times of heavy rain, swamps can help control flooding by acting as basins to collect large amounts of percipitation.
c- Swamps are homes to countless varieties of wildlife, including fish, frogs, insects and reptiles.
d- Many of the plants in freshwater swamps act as "natures kidneys", purifying the water and filtering out harmful pollution.