The International Date Line can be explained as the 180° longitude. The longitude is an imaginary line that runs from the North Pole to the South Pole and helps us to determine our position on the Earth`s surface.

The International Date Line is specifically located at the 180° longitude because it serves as a reference point for determining the date as we travel east or west across it. When one crosses this line from west to east, they skip a day, and when crossing from east to west, they repeat a day. This is done to account for the fact that Earth takes approximately 24 hours to complete a full rotation and ensures that time zones and dates stay synchronized.

Option 1 is incorrect as the equator represents 0° latitude, not the International Date Line.

Option 3 is incorrect as 90° East longitude is a specific line of longitude, not related to the International Date Line.

Option 4 is incorrect as 0° longitude is known as the Prime Meridian, not the International Date Line.

So, in simple terms, the International Date Line is the 180° longitude that helps us determine the date as we cross it from east to west or west to east.