Organizations perform work to achieve a set of objectives. Generally, work can be categorized as either projects or operations, although the two sometimes are（）
（）means that every project has a definite beginning and a definite end.
In approximating costs, the estimator considers the possible causes of variation of the cost estimates, including（） .
The process of（）schedule activity durations uses information on schedule activity scope of work, required resource types, estimated resource quantities, and resource calendars with resource availabilities.
（）involves comparing actual or planned project practices to those of other projects to generate ideas for improvement and to provide a basis by which to measure performance. These other projects can be within the performing organization or outside of it, and can be within the same or in another application area.
