【单选题】

"My own feelings went from disbelief to excitement to downright fear," saysCarl Hergenrother, 23, anArizona undergraduate who verified a large asteroid barreling towardEarth with a 230cm telescope atop nearby Kitt Peak. "It was scary, because there was the possibility that we were confirming the demise of some city somewhere, or some state or small country."

Well, not quite.Early last week, his celestial interloper whizzed byEarth, missing the planet by 450620 km--a hairbreadth in astronomical terms. Perhaps half a kilometer across, it was the largest object ever observed to pass that close toEarth.
Duncan Steel, anAustralian astronomer, has calculated that if the asteroid had struckEarth, it would have hit at some 93460 km/h. The resulting explosion, scientists estimate, would have been in the 3000-to-12000-megaton range. That, says astronomerEugene Shoemaker, a pioneer asteroid and comet hunter, "is like taking all of the U. S. and Soviet nuclear weapons, putting them in one pile and blowing them all up."
And what if one them is found to be on a collision course withEarth Scientists at the national laboratories at Livermore,California, and LosAlamos, New Mexico, have devised a number of ingenious plans that, given enough warning time, could protectEarth from a threatening NEO. Their defensive weapons of choice include long distance missiles with conventional or, more likely, nuclear warheads that could be used either to nudge an asteroid into a safe orbit or blast it to smithereens.
Many people including some astronomers--are understandably nervous about putting a standby squadron of nuclear tipped missiles in place. Hence the latest strategy, which in some cases would obviate the need for a nuclear defense: propelling a fusillade of cannonball-size steel spheres at an approaching asteroiD、In a high-velocity encounter with a speeding NEO, explains GregoryCanavan, a senior scientist at LosAlamos, "the kinetic energy of the balls, would change into heat energy and blow the thing apart."
Some astronomers oppose any immediate defensive preparations, citing the high costs and low odds of a large object’s strikingEarth in the coming decades.But at the very least, Shoemaker contends, NEO detection should be accelerateD、"There’s this thing called the ’giggle factor’ inCongress," he says. "people inCongress and also at the top level in NAS
A、still don’t take it seriously.But we should move aheaD、It’s a matter of prudence."
The world, however, still seems largely unconcerned with the danger posed by large bodies hurtling in from space, despite the spectacle two years ago ofComet Shoemaker-Levy 9 riddling the planet Jupiter with mammoth explosions. It remains to be seen whether last week’s record near-miss has changed any minds.
From the first three paragraphs, we learn that
A、the earth narrowly escaped a catastrophe.
B．one asteroid almost destroyed an entire city.
C．asteroids are comparable to nuclear weapons.
D．the planet earth is vulnerable to dangers.