Final answer:
The YEAR function returns the year within the range of 1900-9999, which accommodates for the Gregorian calendar dates used by most software systems, including the accommodation for the Y2K issue.
Step-by-step explanation:
The YEAR function typically returns the year from the dates it processes within a specific range. This range is set by the software or programming language in which the function is implemented. Historically, and especially in context with the transition from the year 1999 to the year 2000, known as the Y2K issue, the YEAR function in many computer systems returned years in the range of 1900-9999, aligning with most modern Gregorian calendar systems.
The mentioned Y2K problem highlighted the importance of handling years correctly in software to avoid potential chaos in computer systems. It was a coding challenge moving from the 1900s to the year 2000, and dates are based on the common era which has no defined 'year zero'. As such, the correct answer for the range of years that the YEAR function returns is option 4: 1900-9999.