a 和 one在同位结构中的区别

nettalker

九、十月机警中，
...sth, an item(one item) that ...
...sth, one piece of evidence( a piece of evidence) that...

讨论，在上面的同位结构中，an/a 和 one有何差别，哪个更好？道理何在？感觉差不多啊 ！

sbbi

I think should be 'a piece of evidence...", because I saw the similar usage of "..., a fact that".
ANY IDEAS?

nettalker

但平常在国外书面表达中也常见one啊？而且用a感觉也可以 ，可惜手头一时拿不出来