Space Shuttle Project is one of the first huge-typed spaceflight instruments used for many

times in the world, organized by American National Aviation and Spaceflight Bureau, the main researches of【1】are researching and making the system of space shuttle, suggesting and choosing【2】 and landing ports, deciding the scheme of reclaiming the roll booster of solid rocket,【3】the establishment of repairing the roll booster, and rebuilding and expanding the building of the【4】and controlling system.

At the beginning of 1969, the United States set up a group that specially researched the development direction of spaceflight with 【5】 for the next stage,【6】by deputy president. After【7】and research, it suggested that an aero craft with great benefits in【8】should be made, eg【9】the spaceflight being its leading stanchion. In this project, five orbit implements were prescribed to be made, 【10】" Exploitation", " Columbia", " Challenger", "Discovery" and "Atlands".

In 1970, spaceflight got into an all-round【11】of research and manufacture. The whole-project had to delay more than three years. Five orbit implements were【12】to be four and flight experiment for six times was also decreased for four,【13】the number of production was cut down, according to the original scheme. In April 1971 this【14】was decided that Kennedy Space Centre was used for the launching and landing port for space shuttles, and Edwards Air Base was used for the 【15】 landing port. In February 1977,"Exploitation" Orbit Implement started to have entering and landing experiment sin Edwards Air Base. From May 12, 1981 to July 4, 1982, "Columbia" Space Shuttle successfully finished four flight experiments for research and manufacture,【16】meant that the【17】and manufactures were over in【18】form.

It【19】about 12 years and cost more than 75 billion US dollars to finish the whole project. On November 11, 1990, space shuttles began to fly for【20】.

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A．what

B．which

C．where

D．that