Read the following passage and questions, then choose the right answer from options, the answer should be one of A, B, C, D.

<passage>:
The Olympic Gene Pool Why the human race keeps getting faster. 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? What do such trends have to do with athletic performance? Well, if we're living longer and growing up faster, that must mean we're producing bigger, better bodies. Better bodies imply faster miles. We run faster and faster for the same reason it is now common for 11-year-old girls to menstruate. But why are these things happening? Demographers have offered a variety of explanations, but the main one is that our diet is improving. A 12-year-old ate better in 1990 than she would have in the Victorian era. This conclusion is supported by studies of the social elite: Because its members were well-nourished even in the early years of this century, this group has experienced relatively little change, over the past 100 years, in the age girls first menstruate. Another explanation is that health care is getting better. In 1991, according to the WHO, more than 75 percent of all 1-year-olds worldwide were immunized against a range of common diseases. Smallpox, that scourge of previous generations, now is effectively extinct. Probably the best measure of how much healthier we are is the rate of infant mortality, which measures both the health of the mother (a sickly mother is more likely to produce a sickly baby) and the health of the baby. In the past 20 years, infant mortality around the world has dropped from 92 deaths per 1000 live births to just 62. A lot of this can be chalked up to primary-heath-care programs in the developing world--the African average, for instance, has dropped from 135 deaths per 1000 births to 95. But there are also significant improvements in the developed world, with infant deaths dropping in Europe over the same 20-year period from 24 per 1000 live births to just 10. Better health care affects athletic ability directly. This is true in the trivial case in which, say, antibiotics cure a runner's fever before the big race, but it may also be true in a more significant way. Diseases contracted in early infancy can have a lifetime impact on health--not necessarily a big one, but an impact nevertheless. Previous generations bore scars from all sorts of non-life-threatening diseases, the stuff everyone picked up as a baby. Nowadays, though, more and more people grow up with no history of disease. Since top athletes inevitably are drawn from the healthiest sector of the population, a generally superior system of health care means a bigger pool of people to draw from. You are much more likely to find someone who can run a mile in 3:30 in a sample of several million superbly healthy people than you are in a sample of 10,000. The pool of potential athletes has expanded in other ways, too. First, the population has exploded. Second, we are coming ever closer to a worldwide middle class, the class from which athletes typically are drawn. Whether, in an age of multinational capitalism, we may talk reasonably about a post-colonial era is way beyond the scope of this article. The fact remains, however, that the developing world is doing just that--developing. Even Mozambique, which ranks at, or near, the bottom of national per capita gross national product tables, has shown an increase of some 20 percent in adult literacy rates over the past 20 years. Literacy rates are merely an index of education, which itself is another way of talking about a global move away from a hand-to-mouth lifestyle. it's a function of how much more competitive other nations have become. The Olympics originally were the preserve of the socioeconomic elite of the socioeconomic elite among nations. Consider this: Only 13 nations participated in 1896, but there were 172 in 1992. Black Africans didn't take part until the third modern games, held in St. Louis in 1908. Even this was accidental: Lentauw and Yamasami, Zulu tribesmen, entered the marathon because they happened to be in St. Louis as part of an exhibit about the Boer war. Lentauw finished ninth despite being chased into a cornfield by dogs. That doesn't mean, however, that genetic differences in athletic ability can be correlated automatically with race. That is a claim that is impossible to test, because you cannot control, in an experimental sense, environmental differences among the study groups. Sure, you will find more Africans or descendants of Africans standing on the podiums at the end of Olympic track events. And you will find far fewer Asians on those same podiums. But can you, therefore, conclude that Africans have better genes for running than Asians do? No. Environmental differences between the two groups could account for differing levels of athletic success. It is scarcely surprising that Ethiopian or Kenyan distance runners do better than everyone else, since they are in the habit of running immense distances to and from primary school, middle school, and high school. The training is what's crucial, not the blackness. The Chinese sports establishment also has carried out an enormous, and effective, experiment to help dispel the myth that race has a direct relation to athletic ability. Until recently, a quick glance at the medals table confirmed every stereotype people held about Asians and sports. Then the Chinese decided to produce record-breaking female distance runners (and swimmers), and, boy, did they ever. In 1992, China ranked fourth in the Olympic-medal haul. There are some barriers that simply cannot be broken. We will never run a mile at the same speed at which we now run 100 meters, for instance. The laws of oxygen exchange will not permit it. Race horses seem already to have hit that outer limit. For years, they were as good as human athletes at pushing back speed records, but then they simply stopped getting faster. Take the prestigious British Derby. From 1850 to 1930, winning times dropped from 2:55 to 2:39. But from 1986 to 1996, the average time has been--2:39. Unlike people, race horses are specifically bred and reared to run. Generations of careful genetic selection have ensured that today's race horse has every possible speed-enhancing characteristic. Training techniques, too, are tremendously sophisticated. But you can go only so far. You can only breed horses with ultralight thin bones to a certain point

<question>:
According to the article, why do Africans dominate long distance running events these days?

<options>:
A Because African tribes have always held competitions during which the fastest men get the best-looking women as wives, and then they pass on their good genes.
B Because Africans are more willing to suffer than other races, and running a marathon is all about triumphing over physical suffering.
C Because since childhood, African children have had to run a long way from their homes to their schools, so they have the most practice at distance running.
D Because, living in the bush, they have to escape lions and other predators, so natural selection pressure has made them faster.

<answer>:

C