同位语从句除了that还可以用哪些词?

英语中引导同位语从句的词通有连词 that,whether,连接副词 how,when,where等.（注：if,which 不能引导同位语从句.）如:
I have no idea when he will be back．我不知道他什么时候回来.
He must answer the question whether he agrees to if or not.
他必须回答他是否同意这样一个问题.
另外,where,when,why,how,who,what等在引导同位语从句时,一般只用于I have no idea ...结构中,但有人认为,其实这种类型的同位语从句应该列入宾语从句的范畴,因为I have no idea意思就是I don't know ...
如：I have no idea where I should go.
I have no idea how I can get to the railway station