单项选择题 Sacrifices to meet the particular emergency，such as loss of the ship’s tackle through using it for unusual purposes in order to secure her safety in specially difficult circumstances，（）the subject of a general average contribution.

单项选择题 One of the requirements for a general average act is（）.

单项选择题 No jettison of cargo shall be made fair as（）unless such cargo is carried in accordance with the recognized custom of the trade.