The given sentence is missing in the paragraph below. Decide where it best fits among the options 1, 2, 3, or 4 indicated in the paragraph.

Sentence: Productivity gains, once expected to feed through to broader living standards, now primarily serve to enhance returns to wealth.

Paragraph: Economists now argue that inequality is no longer a by-product of growth but a condition of it. ____ (1) ____. Unlike wages, wealth reflects not just income but also access to assets, favourable institutional conditions - such as low interest rates - and public policies like low taxes and housing shortages. ____ (2) ____. In other words, wealth depends on political choices in ways that income currently does not. It’s not just the inequality itself that is the issue but the erosion of mechanisms that once constrained it. ____ (3) ____. Wealth and income inequality are linked, but where wages have stagnated and collective bargaining has weakened, capital income - derived from profits, rents and interest - has been boosted by design. ____ (4) ____.

The paragraph argues that inequality is a feature of modern growth. It explains that because wealth is shaped by assets, institutions, and policy decisions, it grows differently from wages. The paragraph then demonstrates how capital income has been purposefully raised while the mechanisms that once restricted inequality have weakened.

The provided sentence works best at blank 4 because it summarizes the point made immediately before it. The sentence explains the result after claiming that capital income has been "boosted by design" and wages have stagnated: productivity gains now primarily flow to wealth rather than raising living standards. This serves as the argument's obvious conclusion.

Inserting at blank 1 would be premature, as the paragraph hasn't yet explained the distinction between wealth and wages, which the given sentence talks about. Inserting the sentence in blank 2 would interrupt the explanation of how institutions and policy affect wealth. Inserting at blank 3 would interfere with the transition from explanation to consequence because blank 3 comes at a transition point. Therefore, blank 4 is the most appropriate.