SAT OG test7的一道语法题

最简单的方法来理解这道题是,因为后面的短语是修饰作用的,在短语前加一个which is,把短语变从句 .
The information age has ushered children into a global society,which is this situation causing educators to lament a lack of texts that explain the diversity of cultures.
The information age has ushered children into a global society,which is a situation causing educators to lament a lack of texts that explain the diversity of cultures.
另举个例子.
正确：That is my friend,a student reacher her twenties.
That is my friend,this student reaching her twenties.是不是就感觉有点怪了呢?
前面加who is也能判断出来.
That is my friend,who is a student reacher her twenties.
That is my friend,who is this student reaching her twenties.这回应该很明显了吧

"a situation" 是对前面的" a global society"进行解释，是同位语，所以用"this situation"特指是不对的，后者是起代替作用的。而"causing educators..."是situation的定语。
如果分成两个简单句：The information age has ushered children into a global society. ...

this =（上述）这种情况
a = 一种 ，不定指, 因此不合适