Give the reason why the international date line is significant​

In order to avoid the confusion of having different dates in the same country, the International Date Line bends and goes zig zag at the Bering Strait between Siberia and Alaska, Fiji, Tonga and in some other islands.

The International Date Line serves as the "line of demarcation" between two consecutive calendar dates. The International Date Line, shown here as a yellow line, defines the boundary between calendar dates. ... When you cross the date line, you become a time traveler of sorts!

I'm pretty sure it's c. extremely gradual but not 100% sure though.