The last part of this century will be an age of exploration such as man has never know. There are eight planets,(1)___________________________. Their total area is about 250 times that of the earth. Spaceships will not be able to land on some of them but that still leaves to be explored and area ten times as great as the continents of the earth. (2)_____________________. No doubt explorers of the past were terrified by the great empty oceans that lay before them. They conquered their fears 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. (3)______________________. Ever when they travel far beyond the sun they will be able to send messages back.
