Pool Watch Swimmers can drown in busy swimming pools when lifeguards fail to notice that they are in trouble. The Royal Soci

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问题                             Pool Watch
    Swimmers can drown in busy swimming pools when lifeguards fail to notice that they are in trouble. The Royal Society for the Prevention of Accidents says that on average 15 people drown in British pools each year, but many more suffer major injury after getting into difficulties. Now a French company has developed an artificial intelligence system called Poseidon that sounds the alarm when it sees someone in danger of drowning.
    When a swimmer sinks towards the bottom of the pool, the new system sends an alarm signal to a pool-side monitoring station and a lifeguard’s pager. In trials at a pool in Ancenis.near Nantes.it saved a life within just a few months, says Alistair McQuade, a spokesman for its maker, Poseidon Technologies.
    Poseidon keeps watch through a network of underwater and overheard video cameras. AI software analyses the images to work out swimmers trajectories. To do this reliably.it has to tell the difference between a swimmer and the shadow of someone being cast onto the bottom or side of the pool. "The underwater environment is a very dynamic one, with many shadows and reflections dancing around. " says McQuade.
    The software does this by"projecting"a shape in its field of view onto an image of the far wall of the pool. It does the same with an image from another camera viewing the shape from a different angle. If the two projections are in the same position, the shape is identified as a shadow and is ignored. But if they are different, the shape is a swimmer and so the system follows its trajectory.
    To pick out potential drowning victims, anyone in the water who starts to descend slowly is added to the software’s "pre-alert" list, says McQuade. Swimmers who then stay immobile on the pool bottom for 5 seconds or more are considered in danger of drowning. Poseidon double-checks that the image really is of a swimmer, not a shadow, by seeing whether it obscures the pool’s floor texture when viewed from overhead. If so, it alerts the lifeguard, showing the swimmer’s location on a poolside screen.
    The first full-scale Poseidon system will be officially opened next week at a pool in High Wycombe. Buckinghamshire. One man who is impressed with the idea is Travor Baylis, inventor of the clockwork radio. Baylis runs a company that installs swimming pools, and he was once an underwater escapologist with a circus. "I say full marks to them if this works and can save lives, "he says. But he adds that any local authority spending £30, 000-plus on a Poseidon system ought to be investing similar amounts in teaching children to swim.
The word"considered"in paragraph 5 could be best replaced by

选项 A、thought.
B、rated.
C、regarded.
D、believed.

答案B

解析 题目问的是第五段中能替换considered的词是哪个。consider、rate和regard意义基本相同。rate非正式用语。较consider语气弱;regard后需有as,因此有consider的地方可以用rate替换,故选B。
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