1.(1)First degree burns turn white when (they are) pressed.
(2)If burns are on arms or legs, keep them higher than the heart, if (it is) possible.
2.There is no doubt that John's quick thinking and the first aid skills (that/which) he learned at school saved Ms Slade's life.
3.It shows (that) a knowledge of first aid can make a real difference.
探究发现
(1)第1组例句为状语从句的省略。当状语从句的主语和主句的主语一致时,或当状语从句的主语为it,而且从句谓语中含有be动词时,可以把从句的主语和be动词动词一起省略。
(2)例句2为关系代词的省略。当关系代词在限制性定语从句中作宾语时可以省略。
(3)例句3体现的是当及物动词之后跟由连接词that引导的宾语从句时,that可以省略。