If you are talking about the first air pollution problem its is A, almost about 100 years ago.
1955
<span>the correct option is C
</span><span>borders created by imperialist nations have led to modern ethnic tensions
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Modern ethnic tensions were caused by the scramble for and partition of the various spheres of influence often putting often hostile communities into one border, or separating these communities into different states, therefore diminishing their political importance.
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A company called 3M came up with this waterproof sandpaper idea. I think :/