偏差：项目有给定的要操作的某个参数集合，例如成本和质量。
Deviations: a project is given a certain set of parameters within which to operate, such as cost and quality.
进度、成本和质量是工程项目管理的三大控制目标。
Time, cost and quality are the most important control objects of project management.
在这4个变量中，可以修改时间、成本和质量——但范围除外。
From these four variables, fix time, cost, and quality — but not scope.
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