Key: Exercise 1: 1-5:DBACC 6-10:ADBAB 11-15:ADABC 16-20:CD CB B Exercise 2: 1.likely 2.pay a visit 3.particularly 4.properties 5.instruments 6.exploded 7.aliens 8.normally 9.responsible 10.emerge 11.consisted of 12.solve Exercise 3: 1.passing 2.linked 3.objects 4.unfailing 5.wondered 6.in search of 7.survive 8.calendars 9.lunar 10.announcedKey: Exercise 1: 1-5: D B A C C 6-10: A D B A B 11-15: A D A B C 16-20: C D C B B Exercise 2: 1. likely 2. pay a visit 3.particularly 4. properties 5. instruments 6. exploded 7. aliens 8.normally 9. responsible 10. emerge 11.consisted of 12.solve Exercise 3: 1. passing 2. linked 3. objects 4. unfailing 5. wondered 6. in search of 7. survive 8. calendars 9. lunar 10. announced