• Type in the correct tense of the verb in the spaces.
  • Click the button at the bottom to check your answers.
  • Press the "refresh" button on your browser to play again.

be contain trap cover stay melt be call know trap
be be be be encounter release pose agree be be
Scientists say there could something under frozen ground that many deadly diseases. Ancient microbes have been for millennia in the permafrost that large areas of Earth. Permafrost is ground that completely frozen for at least two years. It is common high in mountains and near the North and South Poles. The scientists say the permafrost is because of climate change. The result could the release of unknown, harmful viruses, which scientists are 'Factor X'. Birgitta Evengard, a professor in infectious diseases at a university in Sweden, said we little about Factor X and the biological dangers in Earth's permafrost.

Virologist Jean-Michel Claverie says there viruses deep in the permafrost that more than 50,000 years old. He said these could harmful to humans. Professor Claverie said "ancient viruses up to a million years old" would the most terrifying because they are unknown and we have never them before. He added that deadly bacterial diseases like smallpox and anthrax could be on a large scale. Factor X could even bigger problems. However, many scientists that a bigger danger from melting permafrost the release of methane. This is a greenhouse gas that 80 times more harmful than CO2.

Back to the Factor X lesson.

Share this lesson

More Free Sites by Sean Banville

Online Activities