28. Which of the following can replace the underlined words "a pipe dream"? an impractical idea B. an unforgettable story C. a widespread belief D. a perfect opportunityC 29. How does the successful launch of SpaceX influence people? A. It arouses interest among scientists B. It builds confidence in NASA officials. It causes discussion among average people D. It creates more opportunities for astronauts.B 30. What should be taken into consideration about a space trip according to Levasseur? A. Psychological quality.. Economic capability. C. Educational background. D. Environmental protection. 31. Why does Ruppel mention flight in the last paragraph? review the history of airplane. B. To compare aviation and spaceflight. C. To predict the future of space travel. D. To doubt the possibility of space tourism.