Gap Fill - Factor X - Level 2


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  • After this paragraph, go to Paragraph 2.

   bacteria      dangers      deadly      frozen      infectious      microbes      millennia      mountains      release      viruses   

Paragraph 1

Ancient under frozen ground could contain many diseases. The have been trapped for in permafrost. This is ground that stays completely for at least two years. It is common in and near the North and South Poles. The permafrost is melting because of climate change. The result could be the of unknown, harmful . Scientists are calling these 'Factor X'. A professor in diseases said we know little about Factor X and the biological trapped in Earth's permafrost.

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