Rivers are divided by watershed boundaries, lines that follow the hirght og the loand and the water drians off in the opposite directions. In nature it is virtually impossible to see where oneregion of vegetation starts and ends. Natural vegetation regions gradually change through transition zones.
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Answer:
A fossil fuel is a fuel formed by natural processes, such as anaerobic decomposition of buried dead organisms, containing organic molecules originating in ancient photosynthesis that release energy combustion. We understand today that humanity’s use of fossil fuels is severely damaging our environment. Fossil fuels cause local pollution where they are produced and used, and our ongoing use is causing lasting harm to the climate of our entire planet.
"Estuary" this is where a river meets the sea.