对于句子“This event is taking place at a time when the world is witnessing an unprecedented movement of people from rural areas to cities and other urban centers.”以下哪个意群的划分在视译中更合理呢？

A、This event is taking place// at a time when //the world is witnessing// an unprecedented movement// of people from rural areas //to cities and other urban centers.
B、This event is taking place at a time when// the world is witnessing an unprecedented movement// of people from rural areas// to cities and other urban centers.
C、This event is taking place at a time when// the world is witnessing an unprecedented movement of people from rural areas to cities// and other urban centers.
D、This event is taking place at a time// when the world is witnessing an unprecedented movement of people// from rural areas to cities// and other urban centers.