certainly作“當(dāng)然”解是非正式用語(yǔ),多見于口語(yǔ); 作“必定”解是正式用語(yǔ),口語(yǔ)和書面語(yǔ)均可使用。

　　certainly

　　adv.無(wú)疑;確定;肯定;當(dāng)然;行。

　　The public is certainly getting tired of hearing about it

　　關(guān)于此事，公眾當(dāng)然已經(jīng)聽膩了。