简述公共政策学产生的历史条件。

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。

混交方法是指混交林中各种树种在造林地上配置和排列的形式

树种的混交类型有，主要树种与主要树种混交、（）、（）、主要树种与伴生树种混交。

混交种树的选择条件有（）。

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。

营造混交林成败的关键是造林树种的搭配。