9．From self-driving cars to deep sea explorers，more and more of humans'tasks are being taken over by robots．But technology doesn't stop there．In mid-August，reported the BBC，scientists from Cambridge University developed a robotic system that meant a robot could"build other robots，each one better than the previous（以前的） generation"．
The BBC noted that"those concerned about machines taking over the world shouldn't worry"．
However，over 1，000 scientists and numerous artificial intelligence （AI，人工智能） researchers-including UK astrophysicist Stephen Hawking and Apple cofounder Steve Wozniak of the US-brought the danger of fully autonomous weapons（自主武器），known as"killer robots"，to our attention earlier this summer．
"If any major military（军事的） power pushes ahead with AI weapon development，a global arms race is inevitable（不可避免的），"warned an open letter released at the International Joint Conference on Artificial Intelligence held in Buenos Aires，Argentina．
Unlike drones（无人机），which need a human hand，this kind of robot would have some decision-making abilities and the ability to act by itself．While what the BBC called these"solders that never sleep"could help reduce battlefield deaths，they might also make countries more likely to go into battle，which would lead to more deaths overall，noted the scientists．The risks，they said，could be far greater than those posed by nuclear weapons．
Scientists called for a"ban on offensive（攻击性的） autonomous weapons beyond meaningful human control"，reported The Huffington Post．
In fact，in an interview with the BBC in 2014，Hawking warned that the"development of full artificial intelligence could spell the end of the human race"．
And according to the BBC，many leading thinkers have been thinking about the AI-powered killing machine of the not-too-distant future．"Killer robots could be here within years，not decades，"as Stuart Russell，professor of computer science at UC Berkeley，US，put it．
Authorities are gradually waking up to the risk of robot wars．Last May，for the first time，the United Nations brought governments together to begin talks on so-called killer robots in a hope of stopping such weapons while there is still time．
Meanwhile，there are scientists who are less worried．They believe all technologies have potential（潜力） for being used for good and evil ends，and argue that the ban called for by the open letter could close the door to developing AI technology that could save lives．"Technology can clearly do better than human beings in many cases，"Ronald Arkin，dean at the Georgia Institute of Technology in Atlanta，US，told The Christian Science Monitor．"If we are willing to turn over some of our decision making to these machines，we may actually get better outcomes．"
48．What does Steve Wozniak think the future robot technology might produce？D
A．Artificial Intelligence．
B．Autonomous weapons．
C．Soldiers that never sleep．
D．Killing machines．
49．The underlined word"spell"in Paragraph 7 is closest in meaning to"A"．
A．cause
B．prevent
C．reach
D．change
50．What does Stuart Russell mean by saying"killer robots could be here within years，not decades．"？B
A．Killer robots will visit UC Berkeley，US sooner than expected．
B．Killer robots will be produced and used sooner than expected．
C．Killer robots will speed up the development of AI in the near future．
D．Killer robots will kill these scientists in the near future．
51．What is the main idea of the text？C
A．More and more of humans'tasks are being taken over by robots．
B．Robots have decision-making abilities and the ability to act by itself．
C．Scientists called for a ban on the development of robot technology．
D．All technologies have potential for being used for good and evil ends．
