都可以，具體看實(shí)際要表達(dá)的含義。in the day的意思是在這一天里，強(qiáng)調(diào)的是在這一天的時(shí)間范圍內(nèi)；on the day的意思是在這一天，強(qiáng)調(diào)的是日期。day的基本意思是“一天”，指二十四小時(shí)長(zhǎng)的一段時(shí)間，是可數(shù)名詞。

in the day的例句

It's rather late in the day to say you're sorry the harm's done now.

現(xiàn)在才說對(duì)不起太晚了，危害已成事實(shí)。

We work in the day and rest at night.

我們白天工作晚上休息。

on the day的例句

Inevitably,it rained on the day of the wedding.

果然不出所料，婚禮的那天下起了雨。

"They realized they had heard a thud on the day of the accident,"Denton said.

丹頓說：“他們承認(rèn)在事故發(fā)生的那一天聽到砰的一聲?！?/p>