关系代词引导的定语从句
关系代词所代替的先行词是人或物的名词或代词，并在句中充当主语、宾语、定语等成分。关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。
which, that
它们所代替的先行词是事物的名词或代词，在从句中可作主语、宾语等。
例如：
A prosperity which / that had never been seen before appears in the countryside.
农村出现了前所未有的繁荣。（which / that在句中作宾语）
The package (which / that) you are carrying is about to come unwrapped.
你拿的包快散了。（which / that在句中作宾语）
