阅读下面短文，请从短文后所给各题的4个选项(A、B、C、D)中选出一个最佳选项。 The first astronaut (航天员) to walk in space, Leonov, and his companion, Belaiev, began making preparations for the walk as soon as their spaceship was launched. The spaceship was equipped with a double door, which was fitted with a bellows (风箱) between the ship and the outside. This made it possible for the astronaut, in his space suit with oxygen supply, to go first from the air-filled ship to the bellows. Then the air was let out of the bellows, and while the man stepped outside, the air inside the ship remained at normal pressure. If the door had opened directly into space, the air in the ship would have rushed out and been lost when the door opened. Leonov and Balaiev practiced testing the doors several times after they had begun moving around the earth. When the time came for Leonov to go out, his companion helped him attach the cable that was to keep him from floating away from the ship. Then Leonov entered the bellows, and the door closed behind him. When there was no air left in the bellows, the outer door opened and Leonov could see the blackness of space and the blinding light of the sun. If the sky appears blue to us on earth, it is because the earth‘s atmosphere absorbs a certain number of blue rays of sunlight. Out where there is no air, this phenomenon does not take place. On the earth, our atmosphere spreads light so that, when the sun is up, light seems to be everywhere. However, in the airless outer space, strong lights, such as the sun, exist side by side with a dark similar to the blackest night. The absence of air also explains why the stars do not seem to twinkle (闪烁) in space, as they do from the earth.