下面的短文有15處空白，請根據短文內容為每處空白確定1個最佳選項。(第51-65題，每題1分，共15分)
Rescue Platform
In the aftermath of the terrorist attacks on the World Trade Center,security experts are trying to develop new ways of rescuing people from burning (51)is a platform capable of flying vertically and hovering in the air (52)a platform would rise up and down alongside a skyscraper and pick up people (53)in high stories.
The idea for vertical takeoff platform was hatched(策劃)more than ten years ago by a Russian aerospace engineer,David Metreveli,who has since moved to eveli's design (54)the Eagle,calls for two jet engines that(55)four large horizontal spinning of the propellers (56)the necessary lift,or upward force,to raise the more (57)is supplied to the propellers,the higher the platform(58)Moving the platform sideways involves(59)differing amounts of power to each propeller.
Helicopters are now used in some(60)to get people out of burning pe baskets slung from them dangle beside the building for people to climb into.(61),the baskets cannot reach every floor of a building(62)the ropes from which they hang become unstable(63)a certain length.
So far,Metreveli has built a small-scale model of the Eagle to(64)his the wake of September 11,he has been able to secure enough funding to start building a larger,4-meter by 4-meter prototype,(65)he calls the Eaglet.
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