煤粉在潮模砂的主要作用是防止铸件产生（）缺陷。
A、气孔和砂眼
B、粘砂和气孔
C、粘砂和砂眼
D、夹砂和粘砂
参考答案：D
A work breakdown structure (WBS) numbering system should allow project staff to ______ .
A．identify the level at which individual WBS elements are found
B．identify configuration management milestones
C．estimate the costs of WBS elements
D．provide project justification
设置行间距是在格式菜单中的“段落”命令中进行。（）
