四级练习2012.07.02 thousands, explored, leaves, century, leaves, explored, thousands, century

Rebecca949

The last part of this century will be an age of exploration such as man has never know.
There are eight planets,at least thirty moons and thousands of asteroids to be explored.Their total area is about (1)_______________  that of the earth.Spaceships will not be able to land on some of the,but that still leaves to be explored and area ten times as great as the (2)________________ .
Exploring space may seem terrifying to some people.No doubt explorers of the past were terrified by the great empty oceans that lay before them.(3)_________________ crossed the oceans,and built the New World.In the past when explorers set sail into the unknown they had to say good-bye to all they knew at home.Space explorers will not face such great loneliness.Ever when they  travel far beyond the sun they will be able to send messages back.

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