When economic development takes place in a country over time, how does the share of the tertiary (service) sector in national income generally change according to the usual pattern of structural transformation?

Introduction / Context:
One of the key topics in development economics is structural transformation, which describes how the contribution of agriculture, industry, and services to national income changes as an economy grows. Understanding what normally happens to the share of the tertiary sector (services) as development proceeds is very important for questions related to growth, employment, and policy. This question checks if you know the standard pattern observed in most developing economies as they move to higher income levels.

Given Data / Assumptions:

• The question is about long term economic development, not short term fluctuations.
• The focus is on the share of the tertiary (service) sector in national income.
• We assume the classic three sector model: primary (agriculture), secondary (industry), and tertiary (services).
• Options describe different possible trends over time.

Concept / Approach:
According to the three sector hypothesis and structural change theory, low income economies are dominated by agriculture. As income rises, resources move into manufacturing and industry. At higher stages of development, services such as banking, education, health, transport, communication, tourism, information technology, and trade expand rapidly. As a result, the contribution of services to gross domestic product tends to grow continuously and eventually becomes the largest share of national income in advanced economies.

Step-by-Step Solution:
Step 1: Recall that in poor economies, agriculture has the largest share, with small industry and service sectors.Step 2: As development proceeds, industry expands and agriculture's share falls, while services start to grow.Step 3: In high income stages, services like finance, information technology, advanced health care, and education dominate the economy.Step 4: This means that over the long run, the share of the tertiary sector in national income does not fall; instead, it tends to rise steadily.Step 5: Therefore, the best description is that the share of the tertiary sector keeps on increasing as development takes place.

Verification / Alternative check:
Look at data from many developed countries such as those in Western Europe, North America, and East Asia. In almost all such economies, services account for more than half and often more than two thirds of gross domestic product. Emerging economies like India have also seen continuous growth in the services share over recent decades. This empirical pattern supports the theoretical prediction that the tertiary sector share keeps increasing with development.

Why Other Options Are Wrong:
First falls and then rises: There is no standard stage where the services share falls in the early part of development; it is usually agriculture that declines. This pattern does not match observed data.
First rises and then falls: In modern history, service sector shares have not generally fallen after rising; they remain high in advanced economies.
Remains constant: This is incorrect because structural transformation by definition involves changing sectoral shares, with services rising over time.

Common Pitfalls:
Some learners confuse the trajectory of industry with that of services. Industry often rises and then stabilises or falls moderately as a share, whereas services keep gaining share. Others think that only agriculture changes with development. It is important to remember that the main long term winner in terms of share of national income is the service sector.

Final Answer:
As development takes place, the share of the tertiary sector in national income keeps on increasing.