serious

The teacher looked very serious when she talked about the exam rules.

(Chinese) 老师在谈论考试规则时显得非常严肃。

Are you being serious, or is this just another one of your jokes?

(Chinese) 你是认真的吗，还是这又是你的一个玩笑？

The drought has caused a serious water shortage in the rural villages.

(Chinese) 干旱已导致农村村庄出现严重的缺水问题。

Climate change is one of the most serious challenges facing humanity today.

(Chinese) 气候变化是当今人类面临的最严峻挑战之一。