1、严肃地
... particular 特定的 in all seriousness 严肃地 played by 起作用（过去分词） ...
2、在所有的严重性
in all seriousness » 在所有的严重性 Do you know what an open house is?
3、一本正经
... 大人物important person 一本正经in all seriousness 墓碑tombstone ...
4、极严肃
in all respects 在各个方面 in all seriousness 极严肃，庄重 in all the ages adv literary (throughout history) 本义 历代地，历史上各个朝代地，古往今来 ..
in all apparent seriousness煞有介事
But In All Seriousness但在所有严重性
point out in all seriousness严正指出
In all seriousness very seriously极严肃