英语语法中的名词性从句可以由连接代词（如that, whether, who等）、连接副词（如when, where, why等）和连接形容词（如whether）引导。这些引导词可以用于主语从句、宾语从句、同位语从句等不同类型的名词性从句中，对于理解和正确使用名词性从句具有关键作用。
1. 引导词是连接代词
连接代词包括that, whether, who, whom, whose, what, which等等。这类引导词一般用于引导主语从句或者宾语从句。例如：
- I know [that he is a good student].
- Do you know [whether he is coming or not]?
- [Who will come to the party] is a mystery.
- I don't know [whom he is talking to].
- [Whose book is this]?
- Tell me [what you want].
- Can you tell me [which book you like best]?
2. 引导词是连接副词
连接副词包括when, where, why, how等等。这类引导词一般用于引导地点状语从句、时间状语从句、原因状语从句或者方式状语从句。例如：
- I remember [when we met for the first time].
- She showed us [where she lives].
- Can you tell me [why you are late]?
- Let me show you [how to use this machine].
3. 引导词是连接形容词
连接形容词只有一个，那就是whether。这个连接词主要用于引导同位语从句。例如：
- The question is [whether he will come or not].
