填空题.A. attempt B. charged C. crucial D. delicate E. essentially F. eventually G. expended H. fraction I. individual J. maintain K. minority L. negligible M. scrapping N. slashing O. upsurging Space X launched a cheaper, partially-used rocket into orbit. That's a stride toward 1 the price tag of sending payload to space. Successfully flying reusable rockets is a 2 step toward the dream of sending people to Mars. Until now, rockets have almost all been single-use. Once the fuel is 3 , a rocket stage plummets to Earth, resulting in the destruction of extremely expensive equipment that costs tens of millions of dollars to build. Its founder has likened that to 4 a 747 jet after one flight, which would make air travel impossibly expensive. He has suggested that rocket launches could 5 be much cheaper since the cost of the rocket propellants are less than 1 percent of the full-price ticket for a launch. So, if a rocket could be simply refueled like a jetliner for another flight, the cost of space travel could drop to a 6 of what it is now. The stresses of spaceflight on reused boosters, however, are much greater than those on jetliners. The economics will depend on how many times a booster can be flown, and how much the 7 expense will be to repair the booster each time. Reusable spaceships are not a new idea. NASA's space shuttles were the first real 8 at a reusable spaceship, but the shuttles proved more 9 than hoped, requiring an army of technicians to 10 them between flights. As a result, they ended up being more expensive than expendable rockets.