单项选择题 Masts and derricks of cargo ships are made of（）.

单项选择题 Making cargo plan for appropriate distribution of the cargo on board is（）duty．

单项选择题 Limitation of liability to a specified sum，or a clause totally exempting the Shipowner from liability if the claim is not made within a given time，cannot（）the Shipowner where the loss is due to unseaworthiness unless clear and express words are used to indicate it.