context: The two systems were to run on a trial basis for six months; early television sets supported both resolutions. However, the Baird system, which used a mechanical camera for filmed programming and Farnsworth image dissector cameras for live programming, proved too cumbersome and visually inferior, and ended with closedown (at 22:00) on Saturday 13 February 1937. 
question: BBC ఎంతకాలం వివిధ ప్రసార వ్యవస్థలను ప్రత్యామ్నాయంగా చేసింది?
answers: six months