日出日落是大自然不变的规律。

The rising and setting of the sun are natural ___certainties.

在科学领域，几乎没有什么事情是绝对确定的。

In science, there are very few absolute ___certainties.

尽管面临质疑，他依然对自己的人生选择充满坚定的信心。

Despite doubts, he held onto his ___certainties about his life choices.