题目内容：

It was very long day for children
为什么要加IT WAS A VERY

优质解答

It was a very long day for children.才是正确的.
原因：
day是可数名词,前面要加不定冠词a.was也暗示了后面的名词为单数.
it was a （very) long day 表示“这是（很）漫长的一天”,a不能用the代替.