D The year is 2094. It has been announced that a comet (彗星) is heading towards the Earth . Most of it will miss our planet , but two pieces will probably hit the southern half of the Earth . On 17 July , a piece four kilometers wide enters the Earth’s atmosphere (大气层) with a massive explosion . About half of the piece is destroyed , but the remaining part hits the South Atlantic at 200 times the speed of sound . The sea boils and a huge hole is made in the sea bed . Huge waves are created and spread outwards from the hole . The wall of water , a kilometer high , rushes towards southern Africa at 800 kilometers an hour . Cities on the African coast are totally destroyed and millions of people re drowned . Before the waves reach South America , the second piece of the comet lands in Argentina . Earthquakes and volcanoes are set off in the Andes Mountains . The shock waves move north into California and all around the Pacific Ocean . The cities of Los Angeles , San Francisco and Tokyo are completely destroyed by earthquakes . Millions of people in the southern half of the earth are already dead, but the north won’t escape for long . Because of the explosions , the sun is hidden by clouds of dust , temperatures around the world fall to almost zero .Crops are ruined . The sun won’t be seen again for many years . Wars break out as countries fight for food . A year later , no more than 10 million people remain alive . Could it really happen ? In fact , it has already happened more than once in the history of the Earth . The dinosaurs were on the Earth for over 160 million years . Then 65 million years ago they suddenly disappeared . Many scientists believe that the Earth was hit by a piece of object in space . The dinosaurs couldn’t live through the cold climate that followed and they died out . Will we meet the same end ? 小题1:What is mainly described in the passage ?
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