英语里21日怎么说呢

In Engpsh, the 21st day of the month can be referred to as "the 21st" or "21." For example, you might say "I will see you on the 21st" or "Our meeting is scheduled for the 21st at 10:00am."

It is also common to use ordinal numbers to express dates in Engpsh. For example, you might say "I will see you on the twenty-first of the month" or "Our meeting is scheduled for the twenty-first at 10:00am."

Note that when expressing dates in Engpsh, the day is typically written before the month. For example, the 21st day of the month would be written as "21st" rather than "21."