solemn

这一回应是庄重的，以严肃态度对待问题。

The response is ___solemn, treating the issue with gravity.

这对新人在湖边举行了一场安静而庄严的仪式，交换了戒指。

The couple exchanged rings in a quiet and ___solemn ceremony by the lake.

他向导师郑重起誓，一定会完成那项未竟的研究。

He made a ___solemn vow to his mentor that he would complete the unfinished research.