用when。 关键看从句里缺名词还是副词,名词用that, 副词用when。 本句从句恢复成简单句:He saw his favorite star (on that day), 所以要用when. 如果是这样:I'll never forget the day that we spent together. 这里用that。因为从句:we spent (the days)...
在这里是用when that是关系代词,而when是关系副词。主要区别,通俗的讲,就是关系副词里含有一个介词。 拿你这个例子来说,when=on which。在定于从句中,从句与先行词(the day)需要能够连成一个完整句子。从句本来要说的意思是:He saw his favorite star on the day. 而主句中He will never forget the d...