Read the following carefully and attempt the question.

Historically, the Gaddis have experienced geographical and political isolation and socio-economic deprivation. The economy is largely based on agriculture and allied activities such as sheep and goat rearing.

The process of development of the tribal area of Bharmaur started in the 1970s when Gaddis were included among 'scheduled tribes.' Under the Fifth Five Year Plan, the tribal sub-plan was introduced in 1974 and Bharmaur was designated as one of the five Integrated Tribal Development Projects (ITDP) in Himachal Pradesh. This area development plan was aimed at improving the quality of life of the Gaddis and narrowing the gap in the level of development between Bharmaur and other areas of Himachal Pradesh. This plan laid the highest priority on the development of transport and communications, agriculture and allied activities, and social and community services.

The most significant contribution of the tribal sub-plan in the Bharmaur region is the development of infrastructure in terms of schools, healthcare facilities, potable water, roads, communications, and electricity. But the villages located along the river Ravi in Holi and Khani areas are the main beneficiaries of infrastructural development. The remote villages in Tundah and Kugti areas still do not have sufficient infrastructure.

The social benefits derived from ITDP include a tremendous increase in literacy rate, improvement in sex ratio, and decline in child marriage. The female literacy rate in the region has increased from 1.88 percent in 1971 to 65 percent in 2011. The difference between males and females in literacy level i.e., gender inequality, has also declined.

Tribal sub-plan was introduced in which of the following years?