单选题：根据以下内容回答题：The first astronaut to walk in space，Leonov，and hi

根据以下内容回答题：
The first astronaut 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 di-rectlV into space，the air in the ship would have rushed out and been lost when．the dooropened．
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 bel-lows，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 cer-rain 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．
The spaceship was furnished with a bellows in order to__________ ． A．keep air in the ship when its door was opened
B．prevent the spaceship from floating in space
C．make it possible for the astronauts to walk in space
D．provide the astronauts with air under normal pressure