What is the number of months that have exactly 30 days?

The number of months that have exactly 30 days is four. In the Gregorian calendar, which is the calendar system used by most of the world today, the months of April, June, September, and November each have 30 days.

This answer is rooted in the established structure of the calendar, where every other month has either 31 days or has less than that, specifically February, which has only 28 days in common years and 29 in leap years.

The remaining options suggest incorrect counts, as some incorrectly include months that have 31 days or mistakenly count February. Therefore, recognizing the specific months with exactly 30 days confirms that the answer is indeed four months.