In the Figure Given Below, We See an Expansion of the Production-Possibility

In the figure given below, we see an expansion of the production-possibility curve (from PPC₁ to PPC₂) . The two goods produced are wheat and cloth, which are land-intensive and labor-intensive respectively. The outward shift of the production-possibility curve is likely the result of: $$\text { Wheat }$$

A) a fall in average cost of producing cloth.
B) an increase in the price of cloth.
C) an increase in the size of the labor force, the area under cultivation remaining unchanged.
D) an increase in the national amount of usable land, the size of the labor force remaining unchanged.