With no explanation, label text_A→text_B with either "DON'T KNOW", "NO" or "YES".
text_A: Buoyed by his defeat to Guillemot, Nurmi's races became a series of experiments which he analyzed meticulously. Previously known for his blistering pace on the first few laps, Nurmi started to carry a stopwatch and spread his efforts more uniformly over the distance. He aimed to perfect his technique and tactics to a point where the performances of his rivals would be rendered meaningless. Nurmi set his first world record on the 10,000 m in Stockholm in 1921. In 1922, he broke the world records for the 2000 m, the 3000 m and the 5000 m. A year later, Nurmi added the records for the 1500 m and the mile. His feat of holding the world records for the mile, the 5000 m and the 10,000 m at the same time has not been matched by any other athlete before or since. Nurmi also tested his speed in the 800 m, winning the 1923 Finnish Championships with a new national record. After excelling in mathematics, Nurmi graduated as an engineer in 1923 and returned home to prepare for the upcoming Olympic Games.
text_B: Focusing strictly on Numi's sport of track running, does the passage make it sound like runners have grown more specialized since the 1920s, and thus place less emphasis on trying to set world-beating times in a variety of distances?
YES.