什么时候用定语从句什么时候不用?例The poor boy lost both his parents last year is called Mike.空格里是填还是不填,填的话此句就是定语从句,怎么判断出它是定语从句,如果不填有什么问题?The bridge has been there for nearly fifty years still looks nice .

The poor boy lost both his parents last year is called Mike.这句话应该是The poor boy （who） lost both his parents last year is called Mike.『定语从句要先在句子中找先行词,先行词就是要被修饰的名词,这句话的先行词是the poor boy,（who） lost both his parents last year这句话就是从句,用来修饰先行词the poor boy,你吧括号中的who换成先行词the poor boy 也就是完整的一句话了,也就是说先行词在从句中做主语,而先行词作主语不能省略,所以这里必需要填一个who,下面的那个句子你试试吧 』