他在开始讲演前告诫大家不得心不在焉.用英语怎么说？

他在开始讲演前告诫大家不得心不在焉.

He preceded his speech with a warning against inattention.

he

pron. 他，它，一个人；n. 雄性动物；

例句
Logic had prevailed and he had abandoned the idea.
最终理智占了上风，他打消了那个念头。

preceded

v. 在…之前发生（或出现），先于( precede的过去式和过去分词 )，走在…前面；

例句
The Speaker is preceded by the mace-bearer upon his entry to the chamber.
当议长走进议事厅的时候，前面由执议长权标的人开路。

his

pron. (he的所有格)他的，(he的物主代词)他的东西；det. 属于他的，用于名词前，自己的，指某人的，上帝的；

例句
He claimed that his parents had abandoned him...
他声称父母遗弃了他。

speech

n. 演说，演讲，发言，说话，谈话，说话能力或方式，（乐器的）音，音色，方言，民族语言；

例句
The President declined to deliver the speech himself, on account of a sore throat...
总统因嗓子不适而婉拒了亲自讲话。

with

prep. 和，跟，随着，关于，和…一致；

例句
A waiter entered with a tray...
侍者端着托盘进来了。

warning

n. 警告，征候，预兆，前车之鉴；adj. 警告的，告诫的，引以为戒的；v. 警告( warn的现在分词)，提醒，告诫，预先通知；

例句
Furniture in the classroom should not be changed around without warning the blind child...
教室中的桌椅如需要挪动，应事先告诉这个盲童。

against

prep. 反对，对…不利，紧靠，以防；

例句
His hand brushed against hers; it could have been either accidental or deliberate.
就在有意无意间，他的手轻轻拂过她的手。

inattention

n. 不注意，漫不经心，心不在焉，粗心；

例句
The slightest little bit of inattention can let something slip through.
稍不留神就会让某些东西蒙混过关。