Arrange the sentences in the most logical order to form a coherent paragraph. From the given options (a, b, c, d) choose the most appropriate option.
(i) In an integrated market one country might specialise in a high-wage industry with increasing returns to scale and others in areas in which wages are lower.
(ii) New models of trade do not imply that close economic integration should cause incomes to converge.
(iii) As freer trade expands the size of the market, producers with initial size. advantages outcompete rivals.
(iv) Firms and places are often subject to economies of scale: they become more productive as they grow larger.