The first day of every century must be 1 year, 1 month, 1 day. There is a simple reason. The calendar year starts from 65438+ 1 year 1 month 1. There is no zero year, just like there is no October zero every year.

Therefore, the first year of AD is 1 year, 1 month/day, 1 century is from the first year of AD to 100, and the 2nd century starts from10/year.

10 century began at 100 1, so the 20th century should of course begin at 200 1.

The year 2000 is the last year of the 20th century.

Your teacher's statement is correct in most cases, but it doesn't apply in special years. This statement is to make it easy for you to remember, for example, since the 20th century. Now, what century is 2345? At this time, you can get the 24th century through the teacher's method, but at the same time, according to the concept of textbooks, the first day of the 24th century should be 230 1 year, 1 month, and the year 2300 should still belong to the 23rd century.

Even if there is nothing wrong, the teacher's method is to quickly guess which century the year is in, while the textbook's method is to further verify whether this year is the turn of the century.