Question

leap year
in ancient rome, julius caesar established the 365 - day calendar to match the changing seasons created by the earths movement around the sun. caesar recognized a problem, though: the earth actually takes 365¼ days to circle the sun. the extra one - quarter day would gradually shift the calendar away from the seasons. caesars solution was to add an extra day every four years, in what are now called leap years. caesars math wasnt quite right, though. his approach added too many days. so, in 1582, pope gregory xiii improved on caesars work. he proposed that century years should not be leap years unless they can be evenly divided by four hundred. thus, 1600 would be a leap year, while 1700 would not. pope gregorys calendar, called the gregorian calendar, is still in use today.
what is the main, or central, idea of the passage?
julius caesar created the leap year by adding an extra day to the 365 - day calendar once every four years.
pope gregory xiii improved the calendar by making century years leap years only if they could be divided by four hundred.
the leap year was created in ancient rome to keep the calendar aligned with the earths movements and was later modified by pope gregory xiii.

Explanation:

The passage first mentions Julius Caesar creating the leap - year concept to align the calendar with Earth's movement. Then it talks about Pope Gregory XIII's improvement. The main idea should cover both the origin (Caesar) and the modification (Gregory). The first option only focuses on Caesar's creation, and the second option only on Gregory's modification. The third option includes both the creation in ancient Rome (by Caesar) to align the calendar and the later modification by Pope Gregory XIII.

Answer:

The leap year was created in ancient Rome to keep the calendar aligned with the Earth's movements and was later modified by Pope Gregory XIII.