A、There were no planets without moons. B、There was no air or water on Jupiter. C、Life was not possible in outer space. D、The mys

(20)Since early times, people have been fascinated with the idea of life existing somewhere else besides earth. Until recently, scientists believe that life on other planets was just a hopeful dream. But now they are beginning to locate places where life could form. In 1997, they saw evidence of planets near other stars like the sun. But scientists now think that life could be even nearer in our own solar system.(21)One place scientists are studying very closely is Europa, a moon of Jupiter. Space probes have provided evidence that Europa has a large ocean under its surface. The probes have also made scientists think that under its surface Europa has a rocky core giving off volcanic heat.(22)Water and heat from volcanic activity are two basic conditions needed for life to form. A third is certain basic chemicals such as carbon, oxygen and nitrogen. Scientists believe there might be such chemicals lie at the bottom of Europa’s ocean. They may have already created life or may be about to.(22)You may wonder if light is also needed for life to form. Until recently, scientists thought that light was essential. But now, places have been found on earth that are in total blackness such as caves several miles beneath the surface. And bacteria, primitive forms of life have been seen there. So the lack of light in Europa’s sub-surface ocean doesn’t automatically rule out life forming.
Questions 20 to 22 are based on the passage you have just heard.
20. What did scientists once believe according to the passage?
21. What have scientists found about Europa, a moon of Jupiter?
22. What have scientists come to know recently about the formation of life?