连词代词what, who, which, whose等引导的主语从句。
这些连接代词作用相当于代词，在从句中担当主语、宾语、表语、定语等。
 What we need is more time.
 Who was responsible for the accident is not yet clear.
 Whose book it is not important.
 Which school you want to go matters much.
连接副词when, where, why, how引导的主语从句。
 这些连接副词相当于副词，在从句中充当状语。
 Why he did this is not known.
 When he will come is still unknown.
  It is not known why he did this.
  How he succeeded is unknown to us.
  Where we should hold the meeting needs to be discussed.
注意 wh-引导的主语从句也常用it作形式主语。
也可用whatever,whoever,whomever,whenever,wherever等词引导主语从句，表示“无论什么”、“无论谁”、“无论何时”、“无论在（到）哪里”等。
  Whoever told you to give up smoking was quite right.
  Whatever he gave you should be handed in.
  Whoever told you that was lying.
  Whoever comes is welcome.