吸烟者必须从某天开始突然戒烟，从一天一包烟到再也不抽烟。

One had to quit abruptly on a given day, going from about a pack a day to zero.

youdao

有，一天一包。

Yes, one pack per day.

youdao

或许这是发生那些一天一包烟的烟民或者是早年抽烟抽得很厉害的老烟民的身上。

Perhaps this was one of those pack-a-day smokers or somebody a bit older who smoked heavily in their early years?

youdao