"that"引导的表语从句用于说明主语的内容或状态，通常跟在系动词（如be）后面。在这个结构中，"that"作为连接词，不指代任何具体事物，只起连接作用，且在从句中不充当任何成分。下面是一些"that"引导的表语从句的例句及其讲解：
1. The fact is that he doesn't really try.
讲解：这个句子中，“The fact is”是主句的主语和系动词，而“that he doesn't really try”是一个表语从句，说明了“The fact”的具体内容。
2. The trouble is that I have lost his address.
讲解：在这个句子中，“The trouble is”是主句的主语和系动词，后面的“that I have lost his address”是一个表语从句，说明了“The trouble”是什么。
3. My suggestion is that we should tell him.
讲解：“My suggestion is”是主句的主语和系动词，而“that we should tell him”是一个表语从句，表达了“My suggestion”的具体内容。
4. His sole requirement was （is） that the system work.
讲解：在这个句子中，“His sole requirement”是主语，“was （is）”是系动词，最后的“that the system work”是一个表语从句，说明了“His sole requirement”是什么。
5. My idea is that we should start making preparations right now.
讲解：“My idea is”是主句的主语和系动词，而“that we should start making preparations right now”是一个表语从句，表达了“My idea”的具体内容。
6. That was when I was fifteen.
讲解：在这个句子中，“That was”是主句的谓语，而“when I was fifteen”是一个表语从句，说明了“That”所指的时间。
7. It seems to me the worst comment on dictatorship is that presidents of democracies can laugh, while dictators always look so serious.
讲解：在这个句子中，“It seems to me”是主句的主语和系动词，而“that presidents of democracies can laugh, while dictators always look so serious”是一个表语从句，说明了“the worst comment”是什么。
需要注意的是，在某些情况下，"that"引导的表语从句可以省略，尤其是在非正式文体中或当从句是陈述句时。然而，在正式文体中或当从句需要强调时，"that"通常不会被省略。此外，"that"引导的表语从句通常不使用"if"或"whether"来引导，尽管它们在宾语从句中是可以互换使用的。