Miền
Africa
1
Baltic Sea
1
Belarus
1
Canada
1
Carpathian Mountains Region
1
Central America
1
Chamberlain Farm
1
Chamberlain Farm (Me.)
1
China
3
Developing countries
2
East Asia
1
Effect of human beings on
1
Galapagos Islands
1
Germany
1
Great Basin
1
Great Britain
1
Islamic countries
2
Maine
1
Middle West
1
Nebraska
2
New England
1
New Mexico
1
North America
2
Pakistan
2
Polar regions
1
Portugal
1
Sandhills
2
Sandhills (Neb.)
2
South America
1
Sun
1
Sweden
1
United States
7
Univers
1