Question

when a country decides to non-specialize its products, how come the opportunity cost of producing a certain product stays constant?

Answer 1

Answer - When a country decides to non-specialized, that is, customize its products, the opportunity cost of producing certain stays constant. This is because the cost of producing specialized items decreases, mass production of standardized products enables to achieve economies of production and thereby the opportunity cost of  missing out an alternative by choosing another alternative specialized product is also nullified, There is only one product version and thus opportunity cost decreases due to lack of alternatives.