Scientists have established that influenza viruses taken from man can cause the disease in animals. In addition, man can catch the disease from animals. In fact, a great number of wild birds seem to carry the virus without showing an evidence of illness. Some scientists concluded that a large family of influenza viruses may have evolved in the bird kingdom, a group that has been on the earth 100 million years and is able to carry the virus without contracting the disease. There is even convincing evidence to show that virus strains are transmitted from place to place and from continent to continent by migrating birds.
It’s known that two influenza viruses can recombine when both are present in an animal at the same time, the result of such recombination is a great variety of strains containing different H and N spikes. This raises the possibility that a human influenza virus can recombine with an influenza virus from a low animal to produce an entirely new s
A. H and N spikes are produced
B. animal and bird viruses are combined
C. dissimilar types of viruses recombine
D. two viruses of the same type are contracted
Predictions of many robots in industry have yet come true. For ten years or more, manufacturers of big robots have explained how their machines can make industry mom competitive and productive. The maker for (21) robots is oversupplied now, and the driving force of the robotics(机器人学) revolution is (22) to be with makers of machines that handle a few kilos at most.
"Heavy-robot manufacturers are in some difficulty (23) finding ustomer. They are offering big (24) just to get in the door. There has been a (25) growth everywhere in the numbers of robots, so we admit we are either deceiving (26) or that the market is slowly growing. "said John Reekie, chairman of Colen botics. "The following things must happen (27) the robotics revolution to occur. We must achieve widespread robot literacy(文化), (28) there has been a computer (29) program, there must be a robot prices. (30) , some kind of arti
A. more
B. less
C. no
D. least
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