大学英语：主句隔开；关系代词不可用that

　　1) The sun warms the earth, which makes it possible for plants and animals to live.（太阳温暖了大地，这才使动植物有可能生长。）

　　2) He failed the exam, which made him very disappointed.（他考试没及格，这使他非常失望。）

　　3) He has a son, who is doing his PH.D in the United States.（他有一个儿子，在美国读博士学位。）

　　句中后一个which引导的是一个限定性定语从句，修饰any item。但是传统语法中通常有这样的规定：当先行词是all，everything，something，nothing等不定代词，或被first，only，few，much，some，any，no以及形容词最高级等词修饰时，应该用关系代词that，不用which。例如：I am interested in all that you told me.