Rural settlements are characterized by their location in sparsely populated areas, away from urban centers. These settlements rely on various economic activities to sustain their livelihoods and meet their basic needs. The correct answer to the question is option 'D', which refers to tertiary activities.

Tertiary activities, also known as service activities, involve the provision of services to individuals and businesses. These activities are typically non-productive in the sense that they do not produce tangible goods but rather provide intangible services. In rural settlements, tertiary activities play a crucial role in supporting the local economy and meeting the needs of the community.

Let's explore in detail how rural settlements derive their life support from tertiary activities:

1. Definition and Examples of Tertiary Activities:
- Tertiary activities encompass a wide range of services such as retail, healthcare, education, transportation, tourism, banking, communication, and entertainment.
- In rural settlements, tertiary activities may include small businesses like grocery stores, restaurants, healthcare clinics, schools, transportation services, and tourism-related services.

2. Importance of Tertiary Activities in Rural Settlements:
- Tertiary activities generate employment opportunities in rural areas, allowing individuals to earn a living and support their families.
- These activities provide essential services that meet the daily needs of the local population, ensuring access to goods and services without traveling to urban areas.
- Tertiary activities contribute to the economic development of rural settlements by attracting tourists, creating a market for local products, and fostering entrepreneurship.
- They enhance the quality of life in rural areas by providing healthcare services, educational opportunities, and entertainment options.

3. Role of Tertiary Activities in Rural Development:
- Tertiary activities promote economic diversification in rural settlements by reducing dependence on primary activities like agriculture and mining.
- They help to retain and attract population in rural areas by providing necessary services and improving the overall standard of living.
- Tertiary activities can contribute to the preservation of local traditions, culture, and heritage by promoting tourism and cultural events.
- They facilitate the exchange of goods and services between rural and urban areas, promoting regional development and integration.

In conclusion, tertiary activities are vital for the sustenance and development of rural settlements. They provide essential services, generate employment, and enhance the overall quality of life in these areas. By diversifying the rural economy and promoting local development, tertiary activities play a significant role in ensuring the well-being of rural communities.