不能确定

I doubt if it will rain today.

确定今天是否会下雨。

I myself am unsure how this problem should be handled.

自己确定这个问题应该怎样处。

It is not certain when it will take place.

确定这事什么时候会发生。

I am not sure what value it adds to determining public, or for that matter private, policy.

肯定它对确定公众政此问题而言，对确定个人决增添什么价值。