（）, 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.

When loading or discharging dry mud or cement，crew members should use goggles and（）.

Effects which are dutiable or subject to prohibitions or restrictions should be declared in （）.

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。

时域信号使其变化速度减慢，则低频成分（）概率密度函数是（）域上来描述随机信号的。

离散、周期的时域信号频谱的特点是（）的。

一种信号在频域上是离散频谱，这种信号在时域是周期或准周期信号。

获得非周期时域信号的频谱用（）数学工具。

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。