Question

The writer is considering adding a sentence at the beginning of the passage (before sentence 1):

[1] For centuries, the Julian calendar, introduced by Julius Caesar in $46$ BCE, served as the primary method of tracking time in the Western world. However, the Julian system calculated the solar year as exactly $365.25$ days, which was approximately $11$ minutes and $14$ seconds longer than the actual astronomical year. While this discrepancy seemed negligible in the short term, it accumulated over centuries, drifting by one full day every $128$ years. By the sixteenth century, this error had shifted the calendar by ten days, disrupting the scheduling of Easter and other seasonal festivals.

[2] To address this compounding error, Pope Gregory XIII assembled a team of astronomers and mathematicians led by Aloysius Lilius. In $1582$, the Gregorian calendar was introduced, implementing a refined system for leap years: centurial years would only be leap years if they were divisible by $400$. To correct the accumulated drift, ten days were eliminated from October $1582$, meaning that the day following October $4$ was designated as October $15$. Although met with initial resistance, this system gradually achieved global adoption, aligning human timekeepers with the rhythm of the stars.

Which of the following choices for the proposed sentence most effectively introduces the main topic of the passage?