The correct answer is: B. four times.
After independence, the irrigated area in Bihar enlarged approximately four times. In 1950-51, the net irrigated area in Bihar was 1.7 million hectares. By 1990-91, it had increased to 6.8 million hectares. This increase was due to a number of factors, including the construction of new irrigation canals, the expansion of existing irrigation systems, and the introduction of new irrigation technologies.
The expansion of irrigation in Bihar has had a number of positive impacts. It has increased agricultural production, improved food security, and reduced rural poverty. It has also helped to improve the environment by reducing soil erosion and waterlogging.
However, the expansion of irrigation has also had some negative impacts. It has led to the displacement of people and the loss of biodiversity. It has also contributed to the problem of waterlogging.
Overall, the expansion of irrigation in Bihar has been a positive development. It has helped to improve the lives of millions of people. However, it is important to manage irrigation carefully to avoid the negative impacts.
Option A is incorrect because the irrigated area in Bihar enlarged approximately four times, not two times.
Option C is incorrect because the irrigated area in Bihar enlarged approximately four times, not five times.
Option D is incorrect because the irrigated area in Bihar enlarged approximately four times, not ten times.