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Edmund Halley was an English scientist who lived over 200 years ago . He studied the observations of comets (彗星) which other scientists had made . The orbit of one particular comet was a very difficult mathematical problem . He could not figure it out . Neither could other scientists who dealt with such problems .
However , Halley had a friend named Newton, who was a brilliant (有才华的) mathematician . Newton thought he had already worked out that problem , but he could not find the papers on which he had done it . He told Halley that the orbit of a comet had the shape of an ellipse (椭圆) .
Now Halley set to work .He figured out the orbits of some of the comets that had been observed by scientists . He made a surprising discovery . The comets that had appeared in the years 1531, 1607, and 1682 all had the same orbit . Yet their appearances had been 75 to 76 years apart (相隔).
This seemed very strange to Halley. The different comets followed the same orbit . The more Halley thought about it , the more he thought that there had not been three different comets , as people thought . He decided that they had simply seen the same comet three times .The comet had gone away and had come back again .
It was an astonishing idea ! Halley felt certain enough to make a prediction of what would happen in the future . He decided that this comet would appear in the year 1758. There were 53 years to go before Halley’s prediction could be tested .
In 1758 the comet appeared in the sky . Halley did not see it , for he had died some years before . Ever since then that comet has been called Halley’s comet , in his honor .
67．Edmund Halley figured out the orbit of _______________.
A．some different comets appearing several times
B．the same comet appearing at different times
C．three different comets appearing three times
D．several comets appearing at the same time
68．Halley made his discovery_______________.
A．by doing experiments         
B．by means of his own careful observation
C．by using the work of other scientists     
D．by chance
69．Halley made a surprising , but correct prediction in the year __________ .
A．1704          B．1705        C．1706      D．1707
70．This passage in general is about _______________.
A．Halley and other scientists     B．the orbit of a comet
C．Newton and Halley               D．Halley and his discovery  
71．According to the passage , which of the flowing is NOT true ?
A．Newton figured out the orbit of the comet .
B．Halley figured out the orbit of the comet first .
C．Newton gave Halley some help .
D．Halley died before 1758.