在复合句中充当同位语。
1. that引导同位语从句。
   在下列名词后可用that引导同位语从句answer, belief,doubt, fact, hope, idea, information, knowledge, law, news, opinion, plan, suggestion, thought, truth等。
  I had no idea that you were here.
  The story goes that william killed his wife.
注意
 ①同位语从句引导词that无含义，不充当成分，不可省略。
 ②同位语从句与其说明的名词或代词为同一内容,故可以用is把前边的中心词和从句连接成一个句子。
 ③同位语从句前一般没有逗号。
 that引导同位语从句与引导定语从句的区别：
 that引导同位语从句时只起连接作用，不充当任何成分；
 that引导定语从句时，在从句中要作成分，如主语、宾语等。
 ①He told me the news that our team won.（that引导同位语从句）
 ②The news that / which he told me was very exciting.（that引导定语从句，在从句中作宾语）
2.在no idea, question, problem等后可用wh-疑问词引导同位语从句，if不引导同位语从句。
   I have no idea where he has gone.   i have no idea what he said.
3.辨析:引导名词性从句时what与whatever, who与whoever的区别：
   what 与whatever：
   What you want has been sent here.  ( what = the thing(s) that/all that/anything that特指)
   Whatever you want makes no difference to me.(whatever = anything that泛指)
   What caused the accident was a broken bottle.（特指）
   Whatever caused the accident has not yet been found.（泛指）
   who 与whoever ：
   Who will go to beijing on business has not been decided.(who表疑问，表示“谁”，“哪一个”)。
   Whoever breaks the law should be punished.(whoever = anyone who，表示“无论哪个人”)