《毕金献阅读理解》电子书节选之三_大学英语阅读

《毕金献阅读理解》电子书节选之三

　　The following paragraphs are given in a wrong order. For Questions 21 25, you are required to reorganize these paragraphs into a coherent article by choosing from the list A G to fill in each numbered box. The first and last paragraphs have been placed for you in Boxes. Mark your answers on ANSWER SHEET 1.

　　[A] Spacecraft have to follow a curved path made up of various orbits usually governed by the Sun s gravity. And they need to aim at where their target will be, not where it is when they set off, a task requiring precise navigation to ensure that the vehicle doesn t zoom past its goal and fly for ever into space.

　　[B] Journeys to the stars would be more formidable, because a new speed limit would come into force the speed of light. As Einstein demonstrated, nothing can travel faster than 300,000 km a second. Even if our spaceship could accelerate at 1g until it reached 99 percent of the speed of light, then decelerated at 1g in the final stretch, a trip to our nearest star would take five years and four months.

　　[C] Without air resistance, an object falling from height accelerates at a rate of 9.8m per second every second. Physicists express that acceleration as 1g one times the force of gravity. Space scientists say that a journey in which the craft accelerates at 1g is possibly the limit of human endurance. To guarantee a landing on Mars, the brakes would have to be applied, and the spaceship would need to decelerate at 1g for the second half of the trip. At that rate, the journey would take only forty?nine and a half hours.