下列锅炉压力容器缺陷中最危险的是( )。
A．裂纹
B．变形
C．均匀腐蚀
D．内部沉积污垢
参考答案：A
解析： 下列锅炉压力容器缺陷中最危险的是裂纹。
第二心音逆分裂是指（）
A.呼气时第二心音分裂变明显
B.吸气时第二心音分裂变明显
C.第二心音分裂与呼吸无关
D.多见于二尖瓣狭窄伴肺动脉高压
E.可见于先天性心脏病房间隔缺损
One tool that is useful during both analysis and design is the ______，which is a pictorial representation of the items of infonnation(entities)within the system and the relationships between these pieces of information．
A．data dictionary
B．dataflow diagram
C．use case diagram
D．entity-relationship diagram
