2．In 1801，Giuseppe Piazzi discovered a new object in the sky．He thought it was an undiscovered comet．After further observation，he realized that it behaved more like a small planet than a comet．Piazzi named it Ceres after the Sicillian goddess of grain．Ceres remains the largest known asteroids（小行星）in the sky．It means almost 600 miles（1，000 km） in diameter．By the end of the nineteenth century，several hundred other asteroids had been identified．
Tens of thousands of asteroids have since been discovered，with thousands more found each year．Asteroids are masses of rock and metal that orbit（绕轨道而行）the sun between Mars and Jupiter．They did not form into planets because the perturbations of Jupiter kept them moving too fast to join together．The total mass of all of the asteroids is less than the size of Earth's moon．
Some of the asteroids move in orbits outside the zone between Mars and Jupiter．Asteroids that come relatively close to Earth are known as near-Earth asteroids（NEAs）．Scientists estimate that about 1，000 of these asteroids are 0.6 miles（1km） in diameter．An asteroid of this colliding（碰撞）with Earth would be disastrous．
Scientists have found two sites where giant asteroids struck Earth millions of years ago．One asteroid hit Antarctica about 250 million years ago．Another asteroid struck Mexico's Yucantan Peninsula around 65 million years ago，leaving a hole 112 miles（180km） wide and 1，000 yards （915m） deep．One theory blames the extinction of the dinosaurs on this asteroids's collision with Earth and the climate change that resulted from its impact．
Occasionally，small asteroids strike Earth．These cause little damage．Major collision，such as the one that may have killed the dinosaurs，occur rarely--perhaps only once every 100 million years．
Although the chance of an asteroid striking the planet anytime soon is small，scientists continue to study the orbits of asteroids in the sky．They pay particularly close attention to the asteroids whose paths are close to Earth，and have even landed a spacecraft on an NEA named Eros．Their work helps them learn about the formation of the solar system．It may even help them discover ways to avoid an asteroid disaster in the future．
66．Which of the following statement is NOT true about asteroids？C
A．Asteroids are composed of rock and metal．
B．Asteroids orbit the sun between Mars and Jupiter．
C．Large near-Earth asteroids are sure to strike Earth．
D．A large asteroid colliding with Earth would cause a disaster．
67．The word"perturbations"（paragraph 2）is closest in meaning to"B"．
A．Formation of rocks
B．Disturbance of motion
C．Estimation of scientists
D．Influences of size
68．What scientists have found implies thatB
A．two sites of Earth hit giant asteroids millions of years ago
B．Antarctica was once struck by an asteroid millions of years ago
C．one asteroid left a huge hole in Mexico 250 million years ago
D．the extinction of dinosaurs resulted in asteroid's collision with Earth
69．Which of the following events happened third according to the passage？D
A．Giuseppe Piazzi discovered a new object and name it Ceres．
B．Scientists had a spacecraft land on Eros to learn more about the solar system．
C．Asteroids orbiting the sun failed to form into planets．
D．Several hundred asteroids had been identified by the end of the nineteenth century．
分析 本文主要描述了在宇宙中发现了数以万计的小行星，以及这些小行星可能对地球造成巨大的破坏，而科学家正在观察已避免小行星对地球的撞击．
解答 66．题 C 细节理解题．Asteroids are masses of rock and metal that orbit（绕轨道而行）the sun between Mars and Jupiter 可知A，B正确；An asteroid of this colliding（碰撞）with Earth would be disastrous．可知D正确；C选项太绝对．
67 题B 猜测词意题．根据第二段每年都发现很多小行星，They did not form into planets because the perturbations of Jupiter kept them moving too fast to join together，但是他们都没有形成行星，因为Jupiter 的变动使得他们移动太快而组合不到一起．所以 perturbations 最贴近的意思为Disturbance of motion．
68题B 推理判断题．根据科学家的发现可知，One asteroid hit Antarctica about 250 million years ago，南极洲曾经被小行星撞击过．
69题D 细节理解题．首先提到Giuseppe Piazzi discovered a new object，In 1801，是最先发生的；紧接着提到这些小行星并没有形成行星，They did not form into planets because the perturbations of Jupiter kept them moving too fast to join together．第三提到的在19世纪末，成千上万的小行星被发现识别．By the end of the nineteenth century，several hundred other asteroids had been identified．所以答案选择D．
点评 本文属于科教类阅读文章，学生可能不太感兴趣，比较晦涩．要求考生在平时要多接触宇宙天文地理，带着问题找答案，仔细排除．
