input: Text: The Olympic Gene Pool Why the human race keeps getting faster. By Andrew Berry ( 2,168 words; posted Thursday, July 4; to be composted Thursday, July 11 ) On May 6, 1954, at Oxford University's Iffley Road track, Roger Bannister became, by just half a second, the first man to run a mile in less than four minutes. The Holy Grail of middle-distance running was his. Forty-two years later, however, that achievement seems less significant. Four-minute miles are commonplace; the current record, held by Algerian Noureddine Morceli, is 3:44, more than 5 percent faster than Bannister's speed. What Iffley Road witnessed was just another step along the road to an ever quicker mile, part of the inexorable improvement of athletic performance that we usually take for granted, particularly when the Olympics roll around. If you stop to think about it, though, such constant progress is remarkable. After all, as biomechanical machines with a standard set of parts, humans should be subject to the same limitations we see in, say, automobiles. How come they aren't? A lot of entrepreneurs and technophiles would like us to think that the answer has to do with discoveries in the world of sports technology. A new Nike shoe is trumpeted as something that will shave at least one-thousandth of a second off your 100-meter time. Trainers measure the rate of buildup of lactic acid in your muscles, then claim that their programs will control it. Nutritionists fine-tune athletes
  Question: What does the article posit as the main factor leading to humans running faster and faster over time (as measured in athletic events)?
  
   (A) Humans try harder when there is a goal, and now that there is so much money to be had from sponsorships, athletes just try harder to compete for the money.
   (B) Being raised under conditions that allow humans to get a lot closer to their genetic performance potential.
   (C) A lot more athletes use steroids as part of their training regimes now, legally or illegally. Same reason why some baseball players hit more home runs.
   (D) Natural selection is at work here. The athletes are self-selected, but these improved genes are passed down as the foundation for the next generation.
  Answer:
output: Being raised under conditions that allow humans to get a lot closer to their genetic performance potential.