Why do we have different time zones

As Earth rotates, different parts of Earth receive sunlight or darkness, giving us day and night. Since different parts of Earth enter and exit daylight at different times, we need different time zones. In the late 1800s, a group of scientists figured out a way to divide the world into different time zones.

Due to the earths rotation, different parts of the earth gets sunlight and some don't.

Explanation:

For example if the earth is rotated toward japan, japan will have sunlight and day, and the US for example will be night.

b is the best answer for this question.