单项选择题
The object of plugging holes below the waterline on a ship should be to（）.
A.eliminate all water entering the hole B.only plug holes in machinery or other vital spaces C.reduce the entry of water as much as possible D.plug the largest holes first
单项选择题 The MOST important element in administering CPR is（）.
单项选择题 The most effective first aid treatment for chemical burns is to immediately（）.
单项选择题 The minimum concentration of a vapor in air which can form an explosive mixture is called the（）.
