plain as day 简单明了；显而易见的；清楚明了的

【例句】
His selfishness was plain as day to both haters and supporters of his.
他的自私是显而易见的，无论他的反对者和支持者都同意这一点。

When the new employee started to speak with customers, his natural abilities as a sales man were as plain as day.
当新员工开始与顾客谈话时，他作为推销员的本能充分显露出来。