The correct answer is: A. Lahaul and Spiti
The sex ratio of Scheduled Tribes (STs) in Lahaul and Spiti district is 1000 females per 1000 males. This is the highest among all the districts of Himachal Pradesh. The sex ratio of STs in Kinnaur district is 973 females per 1000 males, while the sex ratio of STs in Kangra district is 964 females per 1000 males. The sex ratio of STs in Shimla district is 957 females per 1000 males.
The high sex ratio of STs in Lahaul and Spiti district can be attributed to the following factors:
- The high literacy rate of women in the district. The literacy rate of women in Lahaul and Spiti district is 80.6%, which is higher than the national average of 65.5%.
- The low incidence of female foeticide in the district. The incidence of female foeticide in Lahaul and Spiti district is very low.
- The strong social and cultural values that promote gender equality in the district.
The high sex ratio of STs in Lahaul and Spiti district is a positive sign for the development of the district. It indicates that the district is moving towards a more equitable society.