an，det.(指初次提及或非特指的人或物)一(个)(一类人或事物中非特指的)任何一(个)(用于前加形容词或后加修饰语的不可数名词之前)一(种)

例句

The media played an important part in the last election.

大众传媒在上一次选举中发挥了重要作用。

as，prep.像如同作为当作

例句

It wasn't quite as simple as I thought it would be.

这事不完全像我想的那么简单。