The correct answer is: C. dendritic
A dendritic drainage pattern is a branching pattern of streams that resembles the branches of a tree. It is the most common type of drainage pattern in the world, and it is found in areas with relatively flat terrain and uniform rainfall. The streams in a dendritic drainage pattern are typically small and shallow, and they flow in a generally downhill direction.
The other options are incorrect because they do not describe the drainage pattern in Bihar plain accurately. A radial drainage pattern is a drainage pattern in which the streams radiate from a central point, such as a mountain peak. A rectangular drainage pattern is a drainage pattern in which the streams flow in a series of parallel lines. A superimposed drainage pattern is a drainage pattern that is superimposed on an older drainage pattern.
The drainage pattern in Bihar plain is dendritic because it is a flat area with uniform rainfall. The streams in Bihar plain are small and shallow, and they flow in a generally downhill direction.