我认为可以肯定地说他会是下一任总统。

I think it's ___safe ___to ___say that he'll be the next president.

或许可以肯定地说，没有用葡萄牙语写成的关于工程学的好书。

It is probably ___safe ___to ___say that there are no good books about engineering written in Portuguese.

根据证据，可以肯定地说这个项目会成功。

Given the evidence, it's ___safe ___to ___say the project will succeed.