On May 17， 2009， according to the plan， Mike Good and I would take a space walk to the Hubble Space Telescope to repair an instrument． The power supply on this instrument had failed， so it could no longer be used． I would be the person doing the repair and Mike my assistant．

    Working in space is more difficult than you can imagine． As there is no gravity， you can't stand and any slight push can result in tragedy ﹣you can be pushed into space， never be back．

    We got to the telescope． Before we could replace the power supply， we would have to remove from the telescope a handrail fixed with four screws． Having taken out the first three， I found the fourth stripped． I realized that the handrail would not come off， which meant we could no longer be able to replace the power supply and repair that instrument， which meant scientists could no longer look at the universe and find life on other planets．

    I tried all kinds of things， and nothing worked． Then Houston， the control centre on the earth， called up and told me to use the tape to tape the bottom of the handrail and pull it off the telescope． They said it was going to take about 27 kilograms of force for me to do that．

    I knew what it meant： The handrail could be completely pulled off and the safety tether might break， and I might therefore be pushed into space．

    Mike was next to me in his space suit but he could not take over my role． I turned and looked into the cabin where my five crewmates were， and nobody in there had a space suit on． However， I knew they were all looking at me． "Come on Mass， we are all behind you．" The telescope must be repaired．

    "Bam!" The handrail came right off． The rest of the walk went well． We finally got the new power supply in． They tried it； turned it on from the ground． The instrument came back to life．

    At the edge of darkness， after about eight hours， I turned around and saw the Earth from our altitude at Hubble， 568 kilometers up． I saw the huge round pure blue globe﹣our home planet． It's the most beautiful， magnificent thing I've ever seen． It's like looking into heaven． It's paradise．

（1）According to the passage， space walk can be very 　　．

A． interesting

B． dangerous

C． comfortable

D． harmful

（2）Mass had difficulty in 　　 when repairing the instrument．

A． fixing the screws

B． getting to the telescope

C． taking off the handrail

D． finding the new power supply

（3）Why did Mass look into the cabin where his five crewmates were？　　

A． To see whether they could help．

B． To find out what they were doing．

C． To ask them to send him a new tool．

D．To let them know what had happened．

（4）What does Mass want to tell us by writing "At the edge of darkness"？ （请用约40词回答）