一周有七天用英语可以说作 "There are seven days in a week."
来源：这是一个固定短语，源自古代罗马人将一周分成了七天。其中，星期天是献给太阳神的，星期一是献给月亮神的，星期二是献给 Mars 的，星期三是献给 Mercury 的，星期四是献给 Jupiter 的，星期五是献给 Venus 的，星期六是献给 Saturn 的。
例句：
I have a busy schedule next week, I have to work every day of the week.
"我下周有繁忙的日程安排，我每天都要工作。"
I usually take a day off on Sundays, since there are seven days in a week.
"我通常在星期天休息，因为一周有七天。"
The store is closed on Sundays, since there are seven days in a week.
"商店星期天关门，因为一周有七天。"