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(1) viany on the products Tumand use louay have the inspirations in Taluit. (2) The airplane is a well-
known example: watching the flight of birds inspired generations of inventors to develop and perfect
aviation technology. (3) Similarly, product developers in the adhesive industry (tape, glue, sticky notes) are
looking to animals for inspiration. (4) The reason is that many naturally occurring animal adhesives are
superior to traditional human-made adhesives.
(5) The tiny hairs on the gecko's feet allow the lizard to adhere to walls and ceilings. (6) The waterproof,
adhesive proteins of zebra mussels make it possible for them to cling to underwater rocks even in the
roughest water conditions. (7) Studies of the "sticking power" of geckos and zebra mussels resulted in the
invention of a product that combines the adhesive properties of the two animals. (8) This product, effective
if used wet or dry, contains tiny pillars designed after gecko hairs as well as an outer coating of adhesive
protein inspired by zebra mussels.
(9) Another recent invention was inspired by the sticky feet of a frog. (10) The adhesive foot pads of the
tree frog are much stickier than most human-made adhesives. (11) The frog's grooved foot pads "self-
clean" by secreting a mucus-like liquid. (12) The stickiness of the foot pad is restored. (13) Inspired by
these foot pads, scientists used silicone oil to boost the sticking power of a grooved adhesive tape they
developed. (14) The resulting product not only clings strongly but can re-stick up to twenty-five times
without weakening.
Question
In the context of the passage, which sentence would be most appropriate to insert after sentence 4
(reproduced below)?
The reason is that many naturally occurring animal adhesives are superior to traditional human-made
adhesives.
O However, human-made adhesives are considered good enough to meet people's needs.
O Animal adhesives are stickier, often reusable, and, in some cases, even waterproof.
O Some animal adhesives have special properties that cannot be replicated in human-made products.
O Product developers in many industries are inspired by elements of the natural world.