| A.Because it worked perfectly. |
| B.Because the right booster was still OK. |
| C.Because nothing serious happened then. |
| D.Because fewer people died in the flight. |
| A.their planes couldn’t fly high in the sky |
| B.they gained much from experience in failure |
| C.their planes were often checked by the experts |
| D.they were unpopular among passengers |
| A.show failure is a better teacher than success |
| B.explain why Challenger failed |
| C.introduce something about Prof Desai |
| D.tell managers how to achieve success |