Search our collection of background (non-event) articles from news media, science journals and other sources.
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19 | 21 |
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6 | 2 | 1 | 4 | 2 | 2 | 4 | 5 | 3 | 8 | 3 |
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United States | 12 | |
Canada | 2 | |
China | 1 | |
Norway | 1 | |
Russia | 1 |