烟草行业安全防范重点是（）.
A.水患
B.火灾
C.安全隐患
D.雷电隐患
参考答案：B
________ twice, the postman refused to deliver our letters unless we chained our dog. (2009北京卷)
A．Being bitten
B．Bitten
C．Having bitten
D．To be bitten
机器和机构有何区别？
