The correct answer is D. Chamba.
The literacy rate in India is 74.04%, as of 2011. The literacy rate in Chamba district is 67.08%, which is lower than the national average.
The following are the literacy rates of the other districts mentioned in the question:
- Mandi: 77.44%
- Hamirpur: 76.23%
- Bilaspur: 78.15%
The low literacy rate in Chamba district can be attributed to a number of factors, including poverty, lack of access to education, and gender inequality. The district has a high proportion of people living below the poverty line, which makes it difficult for families to send their children to school. There is also a lack of schools in rural areas, which makes it difficult for children to access education. In addition, there is a gender gap in education in Chamba district, with girls being less likely to attend school than boys.
The government has taken a number of steps to improve the literacy rate in Chamba district, including building new schools, providing scholarships, and running awareness campaigns. However, more needs to be done to address the root causes of the problem.