when i was boy,the most exciting thing was when to celebrate the Spring Festival.

题目

when i was boy,the most exciting thing was when to celebrate the Spring Festival.
WAS后为什么要加A?为什么不去掉TO,而是WHEN?
and every year more and more people start a stamp collection of their own and discover an interest which can even last lifetime.last前加A，有什么用？
介词后什么情况下加冠词？
as we were all left home at early age.early前加AN可不可以理解为介词后加不定冠词呢？这句话还有毛病吧？

答案

规则是名词作表语时一般要用冠词
因此是I was a boy.(系表结构)
下一个,它的先行词是 thing ,因此要用关系代词(即that,which)而不能用关系副词when,因此把when去掉或改为that.
是last a lifetime吧?last是动词,为什么会在前面加a?
last同样是系动词
prep+n介词短语构成状语,名词后加不加冠词不是语法的,固定用法是怎样就是怎样了
at an early age是固定用法
on a bus=by bus,两种都是固定用法,而前一种用冠词,后者不用