Questions 18 to 20 are based on the passage you have just heard.
18. [A] How spiders gather food.
[B] Why spider webs are so strong.
[C] How spider build their webs.
[D] How new kinds of structures might be designed.
19. [A] They\'re much larger than spiders.
[B] They\'re quite delicate.
[C] They have unusual ways of gathering food.
[D] They developed a long time before spiders.
20. [A] Chemists.
[B] Architects.
[C] Airline pilots.
[D] Auto designers.