The correct answer is: A. 4
Himachal Pradesh was formed on 15 April 1948 as a Chief Commissioner’s Province. It was initially divided into four districts: Chamba, Kangra, Kullu, and Lahul and Spiti. In 1966, the district of Shimla was carved out of the Kangra district. In 1972, the district of Sirmaur was carved out of the Chamba district. In 1979, the district of Solan was carved out of the Shimla district. In 1991, the district of Mandi was carved out of the Kangra district. In 1997, the district of Hamirpur was carved out of the Kangra district. In 2000, the district of Una was carved out of the Hamirpur district. In 2012, the district of Bilaspur was carved out of the Hamirpur district. In 2017, the district of Kinnaur was carved out of the Shimla district. In 2019, the district of Lahaul and Spiti was divided into two districts: Lahaul and Spiti.
Therefore, there were 4 districts in Himachal Pradesh till 1966.