| Reading comprehension. |
| The old belief that the universe never changes is quite wrong. Even before the invention of the telescope, astronomers noticed that bright stars suddenly appeared in the sky and then later disappeared. These stars were called "novae" because they were thought to be new. In fact we now know that they are really old stars which are slowly dying. Novae are old stars which are slowly dying. As they do so they let out huge clouds of material, sometimes as large as the earth, and these explode into space at a speed of about 8 000 000 kilometers per hour. When this happens, the hotter parts of the star become visible, and this is why novae are so bright. Although the explosions are so huge on a human scale, they only consume a small part of the dying star's energy. The death is a slow one and the star may continue to explode for thousands of years. Indeed, there are even some stars which explode once every two weeks. There are other old stars which do not die slowly, but are completely destroyed by one great explosion. These are known as "supernovae". The explosion of a supernovae is equivalent to about a million, million, million, million hydrogen bombs going off at the same time. Just before the explosion the star's density becomes very great and it spins at a very high speed. A matchbox of materials taken from the star at that time would weigh about 1 000 tons and the star would be turning at about 16 000 000 kilometers per hour. The explosion itself occurs suddenly, in the interval of a minute, but the supernovae continues to shine long after the event. One supernovae which Chinese astronomers observed in 1054 can still be seen by us today. It has been shining for at least nine hundred years. |
| 1. Novae were originally thought to be _____. |
| A. stars that disappear suddenly B. stars that explode C. new stars D. dying stars |
| 2. Supernovae are different from novae because _____. |
| A. they are dying stars B. they die gradually C. they can be seen from the earth D. they explode suddenly |
| 3. "As they do so" (line 1, Paragraph 2) means _____. |
| A. as they let out clouds of material B. as they are slowing dying C. as they explode into energy D. as they consume the star's energy |
| 4. The death of a novae is slow because _____. |
| A. each novae only explodes once every two weeks B. the explosion may continue for thousands of years C. each explosion only consumes a little energy of the star D. the novae may continue to shine long after the explosion |
| 5. A matchbox of material taken from a supernovae weigh 1 000 tons because _____. |
| A. the star spins at a very high speed B. the density of the star is very great C. the star explodes all of a sudden D. the star gives off a lot of material |