Прочитайте текст и заполните пропуски A–F частями предложений, обозначенными цифрами 1–7. Одна из частей в списке 1–7 лишняя. Запишите цифры, обозначающие соответствующие части предложений.
Before the invention of the telephone instant communication over long distances was done by a wire-based electric system called the telegraph. Telegraph communication basically consisted of sending series of dots and dashes called Morse code A_________. Although this was a highly successful system back then, it was limited to sending one message at a time, which had to be decoded by an expert in Morse code before a reply could be formulated B________.
In the 1870s, two inventors both independently designed devices that could transmit speech electrically. Alexander Graham Bell was the first to patent his device first and he called it the telephone. Bell's extensive knowledge of the nature of sound and his understanding of music enabled him C________. His idea was based on the principle that several notes could be sent simultaneously along the same wire if they were of differed pitches. Bell then paired up with a young electrician by the name of Thomas Watson and worked on the idea of developing a device D_______.
By 1875 they had progressed significantly and had proven that E________. On 2nd June of that year, Bell mistakenly managed to transmit sound over a wire during an experiment with Watson. By July they had built what was to be the main elements of the telephone. Bell spoke into his instrument, "Do you understand what I say?" and Mr Watson answered "Yes". However, the voice sounds were not very clear F__________. The first successful bi-directional transmission of clear speech by Bell and Watson was made on March 10, 1876 when Bell spoke into the device, "Mr Watson, come here, I want to see you," and Watson answered.
1. different speech tones would vary the strength of an electric current in a wire
2. and sent back to the other side
3. making a telephone call for the first time
4. and still needed some improvements
5. through an electric wire from one place to another
6. to imagine transmitting multiple messages over the same wire at the same time
7. that would transmit human speech
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