certainly作“當然”解是非正式用語,多見于口語; 作“必定”解是正式用語,口語和書面語均可使用。

　　certainly

　　adv.無疑;確定;肯定;當然;行。

　　The public is certainly getting tired of hearing about it

　　關(guān)于此事，公眾當然已經(jīng)聽膩了。