The correct answer is D. Both A and R are true and R is the correct explanation of A.
Bihar is an industrially backward district. This is because there is a lack of infrastructure in Bihar. The lack of infrastructure includes poor roads, power outages, and a lack of skilled workers. These factors make it difficult for businesses to operate in Bihar, which in turn leads to a lack of industrialization.
The reason (R) is the correct explanation of the assertion (A). The lack of infrastructure is the main reason why Bihar is an industrially backward district.
Option A is incorrect because R is true. Option B is incorrect because A is true. Option C is incorrect because R is the correct explanation of A.