it is what preyed on Gatsby ，what foul dust floated in the wake of his dreams that temporarily closed out my interest in the abortive sorrows and short-winded elations of men.
你這句裡面的that是一個特殊情況，它是It is ...that是一整個結構，是強調句型，強調句型的特點是 你把這句的it is 和that去掉後，這句話依然成立。
而你提問的問題應該是問定語從句裡面怎麼區分that的用法。
一般情況下用that 的都是修飾前面的詞，因為代替前面的句子的時候，用的是which。
舉例：This is the best book that I have ever read.
Do you know the things and persons that they are talking about?
The students was late for class 7 times a week, which made her teacher mad.
it is what preyed on Gatsby ，what foul dust floated in the wake of his dreams that temporarily closed out my interest in the abortive sorrows and short-winded elations of men.
你這句裡面的that是一個特殊情況，它是It is ...that是一整個結構，是強調句型，強調句型的特點是 你把這句的it is 和that去掉後，這句話依然成立。
而你提問的問題應該是問定語從句裡面怎麼區分that的用法。
一般情況下用that 的都是修飾前面的詞，因為代替前面的句子的時候，用的是which。
舉例：This is the best book that I have ever read.
Do you know the things and persons that they are talking about?
The students was late for class 7 times a week, which made her teacher mad.