前面用an，例如：

1，An idea suddenly popped into his head.他突然想到了一个主意。

2.He was about to shut the door when an idea came to him.他正准备关门，突然想到一个主意。

3.He already had an idea for his next novel.他已经构思好了下一部小说。

4.It might be an idea to try again later.稍后再试或许是明智的。

idea单数用a还是an 扩展

idea单数用an而不是a.因为idea是想法，主意的意思，idea是可数名词，名词复数是ideas。idea的发音是/aɪˈdɪə/,是以元音音素开头的单词，前面加不定冠词需要用an，而不是a.例如：An idea suddenly popped into his head.他突然想到了一个主意。