Plain意思是“明显的、明白的”。As plain as the nose on your face用来比喻某事显而易见，就像人的脸上都长着一个鼻子，这是人人都看得见的。类似的短语还有as clear as the sun at noonday非常清楚，显而易见。例如：

    —What’s the matter with David recently? He hardly ever answers when he’s spoken to.

    —Good lord—it’s as plain as the nose on your face; his girl friend has jilted him.

    —大卫最近怎么了？和他讲话时几乎没反应。

    —天哪，难道这还不清楚吗？他的女朋友把他甩了。