他对待工作非常严肃。

Tā duìdài gōngzuò fēicháng yánsù.

He treats his work very seriously.

会议室里气氛严肃。

Huìyì shì lǐ qìfēn yánsù.

The atmosphere in the meeting room is serious.

这是一个严肃的问题。

Zhè shì yīgè yánsù de wèntí.

This is a serious issue.