More than a year has passed since the space shuttle Columbia broke into pieces over centra

l Texas. This past January President Bush announced a long-term program of space exploration that would return human beings to the Moon, and thereafter send them to Mars and beyond. As this magazine (Natural History) goes to press, the twin Mars Exploration Rovers, Spirit and Opportunity, are wowing the scientists and engineers at the rovers' birthplace--NASA's Jet Propulsion Laboratory (JPL)--with their skills as robotic field geologists. JPL's official rover Web site is being stampeded by visitors. The confluence of these and other events resurrects a perennial debate: with two shuttle failures out of 112 missions, and the astronomical expense of the manned space program, can sending people into space be justified, or should robots do the job alone？

Modern societies have been sending robots into space since 1957, and people since 1961. Fact is, it's vastly cheaper to send robots: in most cases, a fiftieth the cost of sending people. Robots don't much care how hot or cold space gets; give them the fight lubricants, and they'll operate in a vast range of temperatures. They don't need elaborate life-support systems, either. Robots can spend long periods of time moving around and among the planets, more or less unfazed by ionizing radiation. They do not lose bone mass from prolonged exposure to weightlessness, because, of course, they are boneless. You don't even have to feed them. Best of all, once they've finished their jobs, they won't complain if you don't bring them home.

But there's a flip side to this argument. Back in the late 1960s and early 1970s, in the days of NASA's manned Apollo flights to the Moon, no robot could decide which pebbles to pick up and bring home. But when the Apollo 17 astronaut Harrison Schmitt, the only geologist to have walked on the Moon, noticed some odd, orange and black soil on the lunar surface, he immediately collected a sample. It turned out to be minute beads of volcanic glass. Today a robot can perform. staggering chemical analyses and transmit amazingly detailed images, but it still can't react, as Schmitt did, to a surprise. By contrast, packed inside the 150-pound mechanism of a field geologist are the capacities to walk, run, dig, hammer, see, communicate, interpret, and invent.

And of course when something goes wrong, an on-the-spot human being becomes a robot's best friend. After landing on Mars this past January 3, did the Spirit rover just roll right off its lander platform. and start checking out the neighborhood？ No, its air-bags were blocking the path. Not until January 15 did Spirit's remote controllers man-age to get all six of its wheels rolling on Martian soil. Anyone on the scene on January 3 could have just lifted the airbags out of the way and given Spirit a little shove.

The word "stampeded" (Line 7, Para. ) most probably means ______ .

A．hacked severely

B．clicked frequently

C．closed forever

D．neglected purposely