47、Immediately before going out of the spaceship，the astronauts have to__________ .

　　A.check the spaceship doors

　　B.walk through the bellows

　　C.attach each other with a cable

　　D.do some warm.up exercises

　　48、When he stepped out of the spaceship，Leonov saw__________ .

　　A.black space without light

　　B.the sun first and then darkness

　　C.darkness turning into blinding light

　　D.darkness and light at the same time

　　49、During the day people can see light everywhere，because when the sun is up__________ .

　　A.it gives off light

　　B.it absorbs light

　　C.the earth’s atmosphere gives off light

　　D.the earth’s atmosphere absorbs sunlight

　　50、In outer space，the absence of air is responsible for__________ .

　　A.the brightness of space

　　B.the brightness of stars

　　C.the coexistence of stars and stronger lights

　　D.the coexistence of brightness and darkness