对某事认真be serious后面用介词about 。be serious about 是固定搭配。

例如，他对自己的学习和生活一贯很认真，即使在业余时间里，他也非常严格执行自己制定的学习计划。

For example, he has always been very serious about his study and life, and even in his spare time, he is very strict with his study plan.

beseriouswith***.对人要求严格beseriousaboutsth.对某事要求严格。