A project life cycle is a collection of generally sequential project ______ whose name and number are determined by the control needs of the organization or organizations involved in the project. The life cycle provides the basic ______ for managing the project, regardless of the specific work involved. 一般情况下，随着项目的逐渐进展，成本和人员投入水平呈现出①的态势，而项目干系人对于项目最终产品的特征和项目最终费用的影响会②，变更和缺陷修改的费用通常会③。①、②和③分别是______。