"A week has seven days" 用英语表达为 "A week comprises seven days" 或 "A week is composed of seven days"。
这个短语的来源可以追溯到古希腊和罗马时期，当时人们已经将一周划分为七天。这个短语在英语中已经成为一种固定用法。
例句:
A week comprises seven days and a weekend is two of them.
The calendar year is composed of 52 weeks and 365 days.
A week is made up of seven days, Sunday through Saturday.
翻译：
一周由七天组成，周末是其中的两天。
历年由52周和365天组成。
一周由星期天至星期六的七天组成。