In world-system theory, the relationship between core nations and peripheral nations is sometimes defined as
a. mutual dependence.
c. cyclical.
b. an international division of labor.
d. semiperipheral.

In the world system theory , the relationship between core nations and peripheral nations sometimes described as : B. International division of labor

In the world-system theory, the core nations refer to the countries which is already developed and advanced in technology ( i.e : USA , United Kingdom, Germany)  while the peripheral nation refer to the developing country. The countries from core nations often seek worker from peripheral nations since they can easily get cheaper labor