The last part of this century will be an age of space exploration such as man has never known. There are eight planets, at least thirty satellites, and thousands of small stars to be explored. 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 an area ten times as great as the continents of the earth. 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. They conquered (克服) 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 everyone they knew at home. Space explorers will not face such great loneliness. Even when they travel far away from the earth, they will be able to send messages back. Man will probably explore______.
A．areas on which spaceships can land B．only the largest planets and satellites C．only a few of the large planets D．all the land in space