认真的的英文：demure、douce、sadd、serious、serious-minded、seriousminded、staid。
相关短语：
take .. seriously; take .. for serious 对..认真
intense study 认真的研究
be assiduous in one's duties 认真执行任务
参考例句：
Eleanor was brusque and firm and businesslike.
埃莉诺态度粗暴，意志坚定、办事认真。
We'll get to grips with the problem very soon.
我们将会很快认真处理这个问题。
He carefully read the proceedings from last meeting.
他认真阅读了上次会议的记录。
My son' s reaction to the letter was somewhat indifferent.
我儿子并不认真把这封信当回事。
He did his best, therefore, to achieve a mood half sportive and half thoughtful.
于是他尽其所能培养一种半开玩笑半认真的心情。
I mean it. I'm serious. I'm no kidding!
我是认真的，我没有开玩笑！
I' m in deadly earnest.
我是非常认真的。