**Explanation:**

The correct answer is option **D) Tourism**. In the year 1991, India observed the year as the "Year of Tourism". This decision was taken by the Government of India to promote tourism in the country and enhance its contribution to the economy.

**Reasoning:**

1. **Importance of Tourism:** The government recognized the potential of tourism as a major source of revenue and employment generation. By declaring 1991 as the "Year of Tourism", the government aimed to boost tourism activities and attract more tourists to India.

2. **Economic Impact:** Tourism has a significant impact on the economy as it generates foreign exchange earnings, creates job opportunities, and stimulates growth in related sectors such as hospitality, transportation, and handicrafts. By promoting tourism, the government aimed to boost the economy and improve the living standards of people.

3. **Promotion of India as a Tourist Destination:** The "Year of Tourism" provided an opportunity for the government to highlight the diverse cultural, historical, and natural attractions of India. Various campaigns, events, and initiatives were organized to showcase the country's rich heritage and attract domestic and international tourists.

4. **Infrastructure Development:** To support the growth of tourism, the government invested in the development of infrastructure such as airports, roads, hotels, and tourist facilities. This aimed to provide better connectivity, accommodation, and amenities for tourists visiting different parts of the country.

5. **Awareness and Publicity:** The "Year of Tourism" also focused on creating awareness about the importance of tourism among the general public. The government launched campaigns and promotional activities to encourage domestic tourism and educate people about responsible tourism practices.

6. **Partnerships and Collaborations:** The government collaborated with various stakeholders including tourism boards, travel agencies, hotel associations, and local communities to ensure effective implementation of tourism development plans. This involved the participation of both public and private sectors to leverage their expertise and resources.

Overall, the observation of 1991 as the "Year of Tourism" in India aimed to harness the potential of tourism for economic growth, cultural exchange, and sustainable development. The government's efforts to promote tourism during this period have had a lasting impact on the industry, making it one of the key sectors contributing to India's GDP.