I had-one-day trip in the suburbs during the winter holidays

是B an.你的句子需要一个冠词来修饰 one-day trip.这里的 trip 是单数,但是它的前面已经有了 one-day.所以在前面加 an.意思是一个一天的旅游项目.
I had an one-day trip in the suburbs during the winter holidays.