2. 外语
  3. The idea of television, transmitting pictures through the air or over wires, has been around since the late 19th【B1】______.

The idea of television, transmitting pictures through the air or over wires, has been around since the late 19th【B1】______.

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问题     The idea of television, transmitting pictures through the air or over wires, has been around since the late 19th【B1】______.      But it wasn’t until 1925, when J. L. Baird, a Scottish【B2】______. became the first to electrically transmit moving pictures, that television became a【B3】______.
    Baird’s first television was a mechanical system consisting of several moving parts. It had a small【B4】______ onto which pictures were transmitted 10 times per second at 30 lines of resolution (分辨率). With the help of a photoelectric cell (光电管), bright and dim light were【B5】______ into an electrical signal and sent via radio waves. In June 1925, Baird transmitted the【B6】______ of a human face, winking and smiling from one room of the laboratory to another, without the aid of【B7】______ or wires. Television truly came into its own in the 1930s with the advent of the cathode-ray tube (阴极射线管), which allowed for electronic line-by-line scanning of【B8】______. With the help of the Radio Corporation of America and an improved cathode-ray tube, the first all-electronic TV was demonstrated in 1932.【B9】______.
    As television’s evolution continues, high-definition (分辨率) digital TV is supposed to replace today’s 625-1ine sets with 1,050 or more lines of resolution.【B10】______. This trend has developed very fast.【B11】______.
【B10】
选项
答案Several networks in the Western world have already begun high-definition program broadcasting on some key channels.
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