Interstellar travel, space travel between the stars, has been a staple in science fiction writing for many years. Now, it is being taken seriously by many scientists, who are researching and discussing the possible problems likely to face an interstellar journey. Recently, one research team, affiliated with the Breakthrough Propulsion Physics (BPP) at NASA, has outlined three important breakthroughs that might bring the possibility closer to reality. Firstly, a new propulsion method that consumes much lighter fuels or even massless fuels must be developed. This requirement stems from the fact that current fuels either take up too much space in an interstellar ship or is too heavy to be effectively transported by the ship. Secondly, a propulsion system that attains the maximum speed theoretically possible will be needed due to the vast distances across space. Lastly, NASA sees a need for a breakthrough method of energy production to power the ship’s internal components. The BPP team sees possibilities between the breakthroughs required and past advances in history, such as jet engines replacing the propellers on aircrafts and steamships replacing sailing vessels. In other words, a brand new technology will be needed and is possible when viewed from a historical perspective.
(This passage is adapted from an article from NASA’s webpage.)
【題組】40According to paragraph 2, a lighter or massless fuels have to be created because ______.
(A) the weight and space requirement of current fuel technology are too cumbersome
(B) they have to keep the spaceships smaller
(C) spaceships cost too much to add the mass and the space of heavy fuels
(D) the current fuel technology is one of the effective ways to make a long interstellar journey possible
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