a good news 可以有把握地说,在语法上是错的,因为news是不可数名词.
下面的表达都是对的：
1 It is good news for us all that we will have no school tomorrow.(我们有好消息,明天不上课.)
2 The news is good.
3 This is a good piece of news.
4 This is a piece of good news.