Of course not：当然不

例句：我当然不害怕！

Of course Im not afraid!

certainly not：肯定不是;肯定不会;肯定不

例句：

The students were certainly not wanting in enthusiasm.

学生们当然不乏热情。

Doing it once was just about excusable ─ doing it twice was certainly not.

这种事干一次也许还可以原谅，干两次就绝对不能了。

'I'm certainly not asking him!' she retorted indignantly.

“我当然不是在问他！”她愤然反驳说。

She was certainly not the type to murder her husband.

她绝不是那种会谋杀亲夫的人。