Every year since this year, August 8th is the "National Fitness Day". A. B, D, and D. discuss the nature of the "National Fitness Day. " A said, "All of us in the office know this is not a statutory fitness day. " B said : "If Xiao Zhang says that this is not a statutory fitness activity day, then he considers it to be a statutory 'National Sports Day'. " C said, "Xiao Zhang said that this is not a statutory fitness activity day, nor is it a statutory Beijing Olympic Games memorial. "Ding said," Some people in our office didn't know that it was a legal fitness day, but thought it was a sports festival. "Only one of the four people was known to be untrue. From this:. ['A falsehood.', 'B telling lies.', 'C is telling lies.', 'Ding tells lies.']