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The space shuttle Challenger was supposed to take off on January 22, 1986. Because of bad weather and other problems, though, the launch was put off for several days. When the new launch day arrived, the weather was colder than usual. Some scientists warned that parts of the shuttle might not work well at those temperatures. They were worried about rubber rings, called O-rings, used in the launching rockets. In spite of these warnings, however, Challenger lifted off at 11:39 A.M. on January 28. Less than eighty seconds after liftoff, the shuttle exploded. Later it was found that the O-rings had indeed failed, leading to the explosion.
The Main Idea in this passage is:
The launch of the space shuttle The Challenger was delayed for several days.
Because the O-rings on the challenger didn't work correctly, the space shuttle exploded.
What is Because the O-rings on the challenger didn't work correctly, the space shuttle exploded.