试述平拱砖过梁、钢筋砖过梁、钢筋混凝土过梁三者的优缺点。为什么钢筋混凝土过梁必须有足够的支承长度？前两种过梁的支承长度表现在哪里？

钢筋混凝土预制过梁两端支承在墙上的长度不少于（）。

（）shall be liable for loss of and damage to the Vessel and／or goods arising or resulting from inaccuracies in stating the description，quantity，weight，measurement or contents.

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.

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。

逻辑运算符（AND、NOT、OR）的运算顺序是AND→OR→NOT。