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。
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。
