Why Do Diminishing Rather Than Constant Returns to Specialization Sometimes

Multiple Choice

Why do diminishing rather than constant returns to specialization sometimes occur?

A) All resources are of the same quality.
B) Resources can shift from the production of one good to another seamlessly.
C) Each country has a fixed stock of resources.
D) Different goods use different resources in different proportions.
E) Trade does not affect the distribution of income within a country.