第二部分英语知识运用（共两节，满分30分）
第一节 单项填空（共15小题；每小题1分，满分15分）
请认真阅读下面各题，从题中所给的A、B、C、D四个选项中，选出最佳选项，并在答题卡上将该项涂黑。
16. For our future generations, we must show respect for _______ nature, increasing _______ amount of waste we recycle.
A. the, the B. /, an C. the, an D. /, the
17. The scientist, who successfully cloned a human embryo, proudly presented his new achievement to the related organization, only __________ against this research.
A. being warned B. warned C. having been warned D. to be warned
18. Leaving the car unlocked like that is just an open _________ to thieves.
A. invitation B. access C. solution D. key
19. An overhanging rock offered him a ________ shelter, and hardly had he taken advantage of it when the heavy
