Sunday is the first day of a week.

星期日每一周的第一天。

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During the first week of his stay, he went out one day to do some shopping.

在他刚来的第一周，有一天他出门去购物了。

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What day is the first day of a week?

一周中的第一天是星期几？

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While cyber Monday, the first day of the week after Thanksgiving weekend, has come to be known as the online Black Friday, business was good for online retailers during the holiday weekend.

FORBES: Magazine Article

It was a down day for the markets on this first trading day of the week, as investors are taking a cautious approach due to concerns over the global economy.

FORBES: Afternoon Wrap: AAPL, FB, LEN, QCOR

This was to have been an important, high-energy moment on the first day of the last full week of campaigning.

BBC: The hurricane stealing the candidates' thunder