Complex sentence: The test card was then seen again 17 April 2007 between 4am-5am during the BBC Learning Zone both transmissions were accompanied by a 4-tone test tone, ranging from extremely low frequency to a very high shrill.
Split into simpler sentences: The test card was then seen again 17 April 2007 between 4am-5am during the BBC Learning Zone. Both transmissions were accompanied by a 4-tone test tone, ranging from extremely low frequency to a very high shrill.