By encouraging settlers to move into the Yangtze River valley, the Zhou rulers
(A) provoked centuries of conflict with outside invaders.
(B) produced population growth but also complicated problems of central rule.
(C) promoted the early cultivation of wood pulp for paper products.
(D) promulgated diseases like yellow fever, then kept population growth in check.
(E) programmed future generations of Chinese to obey the dictates of the highly centralized state.
Answer: B