Explanation:

- The river Ganga is a major river that flows through the state of Bihar.

- It geographically divides Bihar into two distinct regions: North Bihar and South Bihar.

- These two parts are often referred based on their location on either side of the river—the areas north of the Ganga and the areas south of the Ganga.

- Let's look at the options:

- Option 1: five (Incorrect, there are not five parts)

- Option 2: three (Incorrect, it's not divided into three parts)

- Option 3: two (Correct. Ganga divides Bihar into two parts)

- Option 4: four (Incorrect, there are not four parts)