We do not see complete specialization in the real world because;

A. not all goods and services are traded​ internationally, production of most goods involves increasing opportunity​ costs, and tastes for products differ.
B. not all goods and services are traded​ internationally, production of most goods involves decreasing opportunity​ costs, and tastes for products differ.
C. not all goods and services are traded​ internationally, production of most goods involves constant opportunity​ costs, and tastes for products are remarkably uniform.
D. all goods and services are traded​ internationally, production of most goods involves increasing opportunity​ costs, and tastes for products are remarkably uniform.