The stories about the long March__ __this is one example ,are well written.填空讲原因翻译

of which, 表示 this is one example of the stories.

of which
前面 the stories about long march 一些有关长征的故事
后面 this is one example 其中的一个例子
这个例子是属于前面stories中的一个，所以是从属关系,所以填of which
The stories about the long March are well written，of which this is one example.

for which