阅读理解。 A few weeks ago, an asteroid (小行星) almost 30 feet across and flying along at 38,000 miles per hour flew 28,000 miles above Singapore. Why, you might reasonably ask, should we care about a near miss from such a tiny rock? Well, I can give you one very good reason: asteroids don't always miss. If even a relatively little object was to strike a city, millions of people could be wiped out. Thanks to telescopes that can see ever smaller objects at ever greater distances, we can now predict dangerous asteroid impacts decades ahead of time. We can even use current space technology and fairly simple spacecraft to alter an asteroid's orbit enough to avoid a collision. We simply need to get this detection- and-deflection program up and running. President Obama has already announced a goal of landing astronauts on an asteroid by 2025 as a pioneer to a human mission to Mars. Asteroids are deep-space bodies, orbiting the Sun, not the Earth, and traveling to one would mean sending humans into solar orbit for the very first time. Facing those challenges of radiation, navigation and life support on a months-long trip millions of miles from home would be a perfect learning journey before a Mars trip. Near-Earth objects like asteroids and comets-mineral-rich bodies bathed in a continuous flood of sunlight- may also be the ultimate resource depots for the human being. To be fair, no one has ever seen the sort of impact that would destroy a city. The most instructive incident took place in 1908 in the remote Tunguska region of Siberia, when a 120-foot-diameter asteroid exploded early one morning. It probably killed nothing except reindeer (驯鹿) but it flattened 800 square miles of forest. Statistically, that kind of event occurs every 200 to 300 years. Luckily, larger asteroids are even fewer and farther between-but think of the asteroid seven to eight miles across that annihilated the dinosaurs (and 75 percent of all species) 65 million years ago. Certainly, when it comes to the far more numerous Tunguska- sized objects, to date we think we've discovered less than a half of I percent of the million or so that cross Earth's orbit every year. We need to pinpoint (定位) many more of these objects and, predict whether they will hit us before it's too late. With a readily achievable detection-and-deflection system we can avoid the dinosaurs' fate. 1. What is the author's purpose in writing the passage? A. To introduce the readers a planetary defense program. B. To prove the necessity of a planetary defense program. C. To show the danger the Earth is facing from outerspace. D. To throw light on the development of space technology. 2. The author believes the detection-and-deflection program can _____. A. send human to Mars B. enable human to survive in deep sea C. help human access resource in space D. predict potential disasters on the Earth 3. The example of Tunguska region is used to show _____. A. a tiny asteroid strike may be destructive B. the danger from space is few and far between C. the detection-and-deflection system is of no use D. the difficulty of predicting the strike of a tiny asteroid 4. We can conclude from the passage that _____. A. it's certain that the Earth will be destroyed someday B. it's vital to set up the detection-and-deflection system C. it's unnecessary to care about the tiny object from the space D. it's possible to put the planetary defense system into use in 2025