回答

・It's so obvious
・Of course

一定是～！的英文可以用 It's so obvious/Of course 來表達。
obvious是形容詞"清楚的、顯然的、明顯的、明白的"的意思。

It's so obvious I know what he feels because we are always together.
『很明顯我知道他的感受，因為我們總是在一起。』

I'm getting married to him tomorrow. Of course, I'm kidding!
『明天我就要跟他結婚了。這一定是個笑話！』

有幫助｜0