天然水及饮用水中主要含有六价硒或四价硒，水样加酸与不加酸保存对测定结果影响不大。
参考答案：对
In schedule development, you create a distribution of probable results for each activity and use it to calculate distribution of probable results for the total project. The technique that you are using is ______ .
A．what-if analysis
B．mathematical analysis
C．Monte carlo analysis
D．resource leveling heuristic
下列哪种病毒的基因组是DNA病毒（）。
A.HAV
B.HBV
C.HCV
D.HDV
E.HEV
