According to Kingsley Davis, migration occurs as result of the following reasons EXCEPT（）

A．Countries paid a heavy price for whichever measure taken.
B．Countries all found themselves in an economic dilemma.
C．Withdrawal of foreign capital resulted in the crisis.
D．Most governments chose one of the two options.

A．Migration exerts a great impact on population change.
B．Migration contributes to mankind's progress.
C．Migration brings about desirable and undesirable effects.
D．Migration may not be accompanied by human conflicts.