6. The ………………. of penicillin, one of the world’s first antibiotics, marks a true turning point in human history A. generation B. exploration C. invention D. discovery 7. The group of doctors has spent 8 months …......…. the side - effects of this new vaccine. A. having examined B. to examine C. examining D. to have examined 8. The doctor said that this disease ………………. prevented by vaccine. A. can B. can be C. could D. could be 9. It’s important _________ wildlife in the area. A. to conserve B. conserving C. conservation D. conserve 10. Japan _________ 40% of its waste every year. A. reuses B. recycles C. refill D. broken 11. The research team decided _________ a video conference to discuss the plan of their next filed work. A. to have B. having C. will have D. have 12. My mother doesn’t mind _________ you a lift when we leave the party tomorrow night. A. to give B. giving C. will give D. give 13. Justine was _____________ to John's birthday party last month. A. invited B. inviting C. invite D. invites 14. Carlos _____________ home before we arrived. A. is going B. will go C. has gone D. had gone 15. Our teeth _____________ at least once a day. A. should clean B. should cleaning C. should be cleaned D. should be cleaning