是on the last day不是in the last day，因为表某日需用介词on，on the last day为固定搭配中文意思是在最后一天

On the last day, I was there with him as he passed away.最后的那一天，我守在他的身边，看着他瞑目而终。

Guests must register in person on the last day of the previous month.