On some projects, especially ones of smaller scope, activity sequencing, activity resource estimating, activity duration estimating, and（）are so tightly linkedthat they are viewed as a single process that can be performed by a person over a relatively short period of time.

正确答案： D

解析： 该题的关键词为"activitysequencing. activity resourceestimating. Activityduration estimating"，其语句结构为"activity sequencing, activity resource estimating, activity duration estimating, and （主语）are so tightly linked（谓语）"，含义为"活动排序、活动资源估算、活动工期估算以及什么紧密相关"，该题考察的知识点在于项目进度管理包含的各个子过程，依次为活动定义、活动排序、活动资源估算、活动工期估算、制定进度计划以及进度监控。考生在了解知识点的前提下能够轻松选出选项D,考生如果缺乏相应的知识，则只能碰运气了。