With respect to urban fertility, it is true that

With respect to urban fertility, it is true that
 
  a. fertility used to be higher than in rural places, but now it is lower.
  b. urban fertility levels in Africa are lower than rural fertility levels in North America.
  c. urban fertility in a country is always at least half the level of rural places.
  d. urban fertility in a country is always lower than rural fertility.

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The urban transition in China demonstrates that
 
  a. governments can retard the urban transition, but cannot stop it.
  b. the one-child policy has helped to slow down the urban transition.
  c. the urban transition is consistent with a Marxian population perspective.
  d. China's largest cities have absorbed most of the growth in the country's urban population.