solemnly

庄严宣誓

To make a formal and serious vow, often in a legal context.

以正式而庄重的方式做出严肃的承诺

郑重承诺

To make a serious and formal promise.

做出严肃而正式的承诺。

To state something formally and with great seriousness.

严肃地说

To speak words in a grave and serious tone.

用庄重严肃的语气说话。

庄严地点头

To move one's head down and up as a sign of agreement or understanding in a serious context.

在严肃的场合下，上下移动头部表示同意或理解。