【单选题】

It can be inferred from the passage that "easy conclusion" (Para. 3 ) is based on the assumptions that
A．people who migrate from rural areas to large cities usually do so for economic reasons

B．most people who leave rural areas to take jobs in cities return to rural areas as soon as it is financially possible for them to do so
C．people with rural backgrounds are less likely to succeed economically in cities than are those with urban backgrounds
D．most people who were once skilled workers are not willing to work as unskilled workers