案例分析题某活动的工期采用三点估算法进行估算，其中最悲观的估算是23天，最乐观的估算是15天，最可能的估算是19天，则该活动历时大致需要（）（1）天，该活动历时估算的方差大概是（）（2）。 空白（1）处应选择（）

单项选择题Which of the following is an important input to scope verification?（）.

A.Work results
B.Historical information
C.Formal acceptance
D.Change request

单项选择题All of followings should be done by the project manager during project control except （）

A.determine that a change has occurred
B.ensure that a change is agreed
C.make sure all changes are approved by management
D.manage changes as they occur