Comets(彗星) are parts of our solar system. Like the planets, they go around the sun.
But comets are not made of solid rocks like planets. A comet is a ball of dust, stones, and ice. Many people call comets dirty snowballs.
The "snowball"may be only a few miles across. But when the sun heats the "snowball,"much of it is changed to gases. The gases spread out and form the comet's head, which may be thousands of miles across.
A comet moves fast in its trip around the sun. But when we see it, the comet does not seem to move. That's because it is so far away. The moon moves fast, but when you look at it, you can't see any motion(运动). That's because the moon is far away.
Each year astronomers(天文学家) discover new comets. Some of them are seen only once. They make one trip around the sun and then go away out into space. The sun's gravity cannot hold them.
Other comets, like Halley, keep returning. They have been captured by the sun. Halley's earliest visit was probably 3,000 years ago. It may keep returning for another 3,000 years.
But every time a comet goes around the sun, the comet loses part of itself. Gases and dust are pulled out of the comet. That's why Halley is now dimmer（暗淡的） than it used to be. Next time it visits us, in 2062, it may be even dimmer. Each visit it may get dimmer and dimmer, until it finally disappears.

“太平天国的历史作用不在于‘运动’本身‘革命’，而在于引发了‘生死竞争’，迫使不同营垒中的开明之士顺应历史发展方向。”该观点认为太平天国运动（    ）

“太平天国的历史作用不在于‘运动’本身‘革命’，而在于引发了‘生死竞争’，迫使不同营垒中的开明之士顺应历史发展方向。”该观点认为太平天国运动（    ）

设x*y定义为x*y=（x+1）（y+1），x^*2定义为x^*2=x*x．则多项式3*（x^*2）﹣2*x+1在当x=2时的值为（　　）