Since they were first observed more than 35 years ago by satellites, these bursts of energy have been one of the biggest mysteries of space. Where do they come from? Why do some bursts last only a fraction of a second while others last a few minutes? Ks5u

　　If a star is big enough, it collapses into a black hole when it runs out of fuel. A black hole is a dense and dark object with gravity so strong that not even light can escape from it. Many astronomers believe that as the star fades away and becomes a black hole, it shoots gamma rays into space. In other words, if you had seen the gamma-ray burst last September, you might also have been watching the birth of a powerful black hole. Ks5u

　　The first observations from the Fermi telescope are helping scientists answer questions about gamma-ray bursts. But as the data comes in, and astronomers learn more about these deep-space fireworks, other questions will arise. That’s the nature of good science — the answer to a question leads to another question, and its answer leads to yet another question that needs to be answered. Ks5u

　　51. Which of the following statements is true? Ks5u

　　A. Gamma-ray bursts are unable to be observed. Ks5u

　　B. Gamma-ray bursts are really brilliant flashes of light from explosions. Ks5u

　　C. The gamma-ray burst that occurred last September is not the strongest explosion ever seen. Ks5u

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