To be extremely serious and proper in demeanor or manner; to put on a solemn, grave air.
尽管周围的人都在说笑，他依旧作古正经地坐在那里，仿佛有什么重要的事情要思考。
Although everyone around was laughing and joking, he remained seated with a serious and solemn expression, as if contemplating something important.
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