Time is in the year 2095．It is reported that a comet（彗星） is rushing towards the Earth．Most of it will miss our earth，but two pieces will probably hit the southern half of our planet．

On 15July，a piece about four kilometers wide enters the Earth's atmosphere（大气层） with a massive（巨大的） explosion（爆炸）．About half of the piece is destroyed but the remaining part hits the South Atlantic at 200times the speed of sound．A hole is made in the sea bed．Huge waves spread outwards from the hole．The wall of water，a kilometer high，rushes towards southern Africa at 800kilometers an hour．Cities on the African coast are totally destroyed and millions of people are drowned（淹死）．

Before the waves arrive in South America，the second piece of the comet hits Argentina．Earthquakes and volcanoes（火山爆发） are set off in the AndesMountains（安第斯山脉）．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 it for long．Because of the explosions，the sun is hidden by clouds of dust（灰尘），temperatures around the world fall to almost zero．Crops are destroyed．The sun won't be seen again for many years．Wars break out as countries fight for food．A year later，no more than 10million 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 160million years．Then 65million 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？

42．When the first piece hits the South Atlantic，it causes___．

A．an earthquake

B．volcanoes

C．an Earth explosion

D．huge waves

43．Why can't the