深入了解定语从句中that的省略规则：
在引导定语从句时，that作为关系代词的妙用在于，当它充当宾语时，通常可以被省略。无论先行词是特定的名词还是像'all'这样的不定代词，这一原则依然适用。例如：
原句： The book that I read yesterday was very interesting.
省略后： The book I read yesterday was very interesting.
然而，关键在于，当that在定语从句中担任主语时，绝对不能省略，因为它在句子结构中扮演着至关重要的角色，以保持清晰的语法结构。比如：
原句： The person that everyone admires for his kindness is our teacher.
正确表达： The person that everyone admires for his kindness is our teacher.
通过以上分析，我们可以看出that在定语从句中充当主语时的不可或缺。希望这些规则能帮助你在英语写作中运用定语从句时更加游刃有余。