the way (in which)the words are used is very important.为什么不是in that,which
问题描述：
the way (in which)the words are used is very important.为什么不是in that,which
答
1、关于which和in which
因为在定语从句中 in which是use的方式状语,所以单独的名词或代词不能作状语,而in which这一介宾短语结构恰恰可以作方式状语,故此要用 in which（in必须保留）,但美式英语中经常把in which省掉.
2、关于in which和in that
理论上讲in which和in that本质上没有什么不同,但英语中习惯于把in which用在类似于您提到的这样的定语从句中（which兼作方式状语中介宾短语中的宾语）,而偏偏习惯于把in that当成because来理解,也就是说in that()这个介宾短语作补语.本质上讲,that后面的内容是that的同位语,in that的本义就是”在那个事情上“,例如：She was fortunate in that she had friends to help her（因为有朋友帮她所以她很幸运,在有朋友帮她这件事情上她是幸运的）