一般为a e i o u开头的词，不过是元音音素开头的词前加an，例如：
1.One group was asked to seek out an interaction with its waiter the other， to speak only when necessary ．一组被要求主动跟服务员互动另一组只在必要时发言。
3.An Interaction Study of China's Foreign Trade Structure and Industrial Structure.我国对外贸易结构与产业结构的互动性研究。
