煤矿井下供电及电气设备应做到“三无”，即（）、（）、（）。
参考答案：无鸡爪子、无羊尾巴、无明接头
Models drawn by the system analysts during the process of the structured analysis are （75） .
A．PERTs
B．ERDs
C．UMLs
D．DFDs
. As a new graduate, he doesn’t know_______it takes to start a business here.
A．how
B．what
C．When
D．which
