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  3. A blind baby is doubly handicapped. Not only is it unable to see, but because it cannot receive the visual stimulus from its env

A blind baby is doubly handicapped. Not only is it unable to see, but because it cannot receive the visual stimulus from its env

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问题     A blind baby is doubly handicapped. Not only is it unable to see, but because it cannot receive the visual stimulus from its environment that a sighted child does, it is likely to be slow in intellectual development. Now the ten-month old son of Dr. and Mrs. Dennis Daughters is the subject of an unusual psychological experiment designed to prevent a lag in the learning process. With the aid of a sonar-type electronic that he wears on his head, infant Dennis is learning to identify the people and objects in the world around him by means of echoes.
    The device is a refinement of the "Sonicguide", an instrument produced by Telesensory Systems, Inc., of Palo Alto, Calif., and used by blind adults in addition to a cane or guide dog. As adapted for Dennis, it consists of a battery-powered system about the size of a half dollar that is on a headgear. A transmitter emits an ultrasonic pulse that creates an 80 degree cone of sound at 6 feet. Echoes from objects within the cone are perceived as sounds that vary in pitch and volume with the size and distance of the object.
    The closer an object is, the lower the pitch, and the larger the object, the louder the signal. Hard surfaces produce a sharp ping, while soft ones send back signals with a slighdy fuzzy quality. An object slightly to the right of Denny’s sends back a louder sound to his right ear than to the left. Thus, by simply moving his head right and left and up and down, he can not only locate an object but also get some notion of its shape and size, thanks to the varying qualities of sounds reaching his ears as the cone of ultrasound passes its edges. Dennis likes to use the device to play a kind of peek-a-boo with his mother. Standing on her knee and facing her directly, he receives a strong signal in both ears. By turning his head away, he makes her seem to disappear. "From the first time he wore it," says Mrs. Daughters, "it was like a light going on in his head."
    What remains to be determined is how well the device will help Dennis cope with his surroundings as he begins to walk and venture further into his environment. Meanwhile, Telesensory, Inc. is working on the development of sonar device with somewhat the same sensitivity as Dennis’s for use by school-age children.
In the 5th line of the third paragraph, "its edge" refers to _______.
选项 A、the edge of an object
B、the edge of the device
C、the boundary of Dennis’ movement
D、the boundary of the sound pitch
答案A
解析 第3段第4句中的thanks to表明此处解释了Dennis的声纳定位仪的运作机制，即通过声波描绘物体的形状，该句中the cone指的就是该定位仪，而its edge应指周围物体的边缘，当声波碰到物体的边缘时．就能通过声音描绘出物体的形状了，因此本题答案应为A。
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