他鄭重保證要做得更好英文怎麼說？

He made a solemn promise to do better.

就職典禮是一件隆重的大事英文怎麼說？

The inauguration was a solemn event.

政府發表了一項嚴正的聲明英文怎麼說？

The government made a solemn statement.

總統正式宣誓就職英文怎麼說？

The President took the solemn oath of office.

他很嚴肅,沈默寡言英文怎麼說？

He was very solemn and refrained from talking.