the average number of people living in a square mile or a square kilometer
a land area nearly surrounded by water
a large raised area of mostly level land bordered on one or more sides by steep slopes or cliffs
a river or stream that flows into a larger river
wide and deep enough for ships to travel through
the area on the dry, sheltered side of a mountain, which receives little rainfall
the grasslands of fertile soil suitable for farming in Russia
a cold, dry, treeless region covered with snow for most of the year
a permanently frozen layer of ground below the top layer of soil
a type of rich, dustlike soil
the power generated by water-driven turbines
a source of energy that forms from the remains of ancient plants and animals
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