定语从句:It is the knife that made you out of trouble.
主语从句:Whether that is possible does not have any needs to be judged by the manager.
宾语从句:I think that is a good idea.
表语从句:The problem is what that costs.
同位语从句:The question whether that is a UFO has just been discussed.
补足语从句:I do not know whether that is dirty,but I made the city where that is everywhere.(注意后半句才含有宾语补足语从句)
状语从句:If that is nice,I will introduce that to my friend.
但只有定语从句中的that才可能既做主语,又是引导词.