输出到数据总线的电路都应是可控的三态门电路（或类似功能的电路），为什么？

何谓三态门？何谓OC门？这种电路是如何使用的？

图 3.3 所示三态门, EN 为 使能端,当 A=1 , EN =0 时, 输出为
图3.3

 三态门输出高阻状态时,下面说法不正确的是 (       )

输出继电器（OR）通过一对（）触点将PLC的控制信号传递给负载。

Every deliberate act of wrongdoing by the master or any of the crew against the ship or cargo，without the authorization or privity of the Shipowner or his agent，is（）.

（）, or drum is used for hauling in or letting out the wires or ropes which will fasten the ship to the shore.

A salvor may be（）the whole or part of the payment due under Salvage Convention to the extent that the salvage operations have become necessary or more difficult because of fault or neglect on his part or if the salvor has been guilty of fraud or other dishonest conduct.

The （） is used for hauling in or letting out the wires or ropes.

Vessels must be（）valid certificate of nationality or certificated of registry or license.

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。