老师严肃地说，大家要认真学习。
lǎoshī yánsù dì shuō ， dàjiā yào rènzhēn xuéxí 。
The teacher said sternly that everyone must study seriously.
在这个场合，我们需要保持严肃。
zài zhègè chǎnghé ， wǒmen xūyào bǎochí yánsù 。
In this occasion, we need to maintain solemnity.
他的表情非常严肃。
tāde biǎoqíng fēicháng yánsù 。
His expression is very serious.