题目内容：
请根据短文内容，回答题。 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 skyscrapers. One__________ (51) is a platform capable of flying vertically and hovering in the air__________ (52) a helicopter. The 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 (策划) more than ten years ago by a Russian aerospace engineer, David Metreveli, who has since moved to Israel. Metreveli's design__________(54) the Eagle, calls for two jet engines that__________ (55) four large horizontal propellers. The spinning of the propellers __________(56) the necessary lift, or upward force, to raise the platform. 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 building. Escape 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 idea. In 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.
_________ A．idea
B．skill
C．building
D．improvement
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