The figure given below represents the effects in the labor markets due to migration. Here the world has been divided into a high-income “North” (left panel) and a low-income “South” (right panel). D n and S n are the labor demand and the labor supply curves in North. D s and ( S r + S mig ) are the labor demand and pre-migration labor supply curves in South. S r is the post-migration labor supply curve in South. The value c is the cost of migrating. 8 0 90 12 0 14 0 1 1 0 130 0 0 6.75 8.00 Wages ($ per hour) ( S r + S mig ) Workers ( millions ) Workers ( millions ) a b c e f D n S r N orth S outh Wages ($ per hour) S n 3.00 4.25 D s d T he world's net gain due to migration is represented by the area: a. ( a + b ). b. ( e + f ). c. ( a + f ). d. ( b + f ).