The heart of effective time management is in weekly time organization; ________, you also need a semester long calendar to lay ________ all of your major obligations.
句意：有效时间管理的核心是对于每周时间的组织；然而，你也需要一个学期日历来列出你所 有的主要任务。上下两句为转折关系，因而使用转折词however。lay out展示；安排。故选B。