This study also found that serious head injuries also increased a person's risk.

VOA: special.2009.04.07

This was serious study.

这是一项非常严谨的研究。

哈佛公开课 - 幸福课课程节选

If you're a serious chess player, you might study some of the great games of chess history.

如果你是一名严谨的棋手,你可能还会研究国际象棋史上最伟大的棋局

耶鲁公开课 - 死亡课程节选