可以肯定的说英文

It is sure that

More people are aware of that health and happy are the most important things than ever before.

I can say for certain that...三楼错误。三楼写的 I can firmly/definitely/surely tell you that ...意思是，“我肯定能告诉你”，跟“我可以肯定地说”意思是不一样的！二楼语法错误。四楼用词别扭。倒是一楼的还算不错。：)

I can say for sure that 。。。

I could surely to say that......