同学你好，该知识点来自沪江网校《英语零基础直达大学六级【随到随学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好~
“One of the +复数名词”后面定语从句中谓语动词通常用复数形式，跟定语从句所靠近的那个复数名词在数上保持一致。
This is one of the stories that were written by him. 这是他写的其中一部小说。

如果one of +复数名词这一结构前面带有the only、the very之类的限定语，后面定语从句的谓语动词则要用单数形式，这是因为定语从句在意义上修饰的是one而不是那个复数名词。如：
This is the only one of the stories that was written by him. 在这些小说中，这是他写的唯一一部。

又如：

1. Tom is one of the boys who were praised by the headmaster yesterday.
汤姆是被校长表扬的男孩中的一个。
2. Tom is the only one of the boys who was praised by the headmaster yesterday.
在那些孩子中，汤姆是受到校长表扬的唯一一个。

所以这里选择that have been shown，因为这里没有the only等词修饰one

祝同学学习进步~