Once I invited a group of friends round to my house, telling them that I was going to record their speech. I said I was interested in their regional accents, and that it would take only a few minutes. Thus, on one evening, three people turned up at my house and were shown into my front room. When they saw the room they were a bit alarmed, for it was laid out as a studio. In front of each easy chair there was a microphone at head height, with wires leading to a tape-recorder in the middle of the floor. I explained that all I wanted was for them to count from one to twenty. Then we could relax and have a drink. I turned on the tape-recorder and each in turn seriously counted from one to twenty in their best accent. When it was over, I turned the tape-recorder off and brought round the drinks, and for the rest of the evening there was general cheerful conversation--interrupted only by the fact that I had to take a telephone call in another room, which unfortunately lasted some time. Or at least that was how it would appear. For, of course, the microphones were not connected to the tape-recorder in the middle of the room at all but to another one, which was turning happily away in the kitchen. The participants, having seen the visible tape-recorder turned off, paid no more attention to the microphones which stayed in front of their chairs, only a few inches from their mouths, thus giving excellent sound quality. And my lengthy absence meant that I was able to obtain as natural a piece of conversation as it would be possible to find. I should add, perhaps, that I did tell my friends what had happened to them, after the event was over, and gave them the choice of destroying the tape. None of them wanted to--though for some years afterwards it always seemed to be my round when it came to the buying of drinks. Linguistic research can be a very expensive business. The writer turned off the tape-recorder because   _  .
he had to answer a phone call he wanted his friends to enjoy some drinks he thought the tape-recorder might bother his friends he wanted to make his friends believe he had finished the recording