Which of the following statements is (are) correct?

I.The economic justification for nations to trade owes to the notion ofcomparative advantage.

II.According tocomparative advantagecountries should focus on producing what they are best at and trade for the other products or services.

III.According tocomparative advantagecountries would be limited to the goods and services produced within their own borders without trade.

IV.Economic arguments for comparative advantage were developed by John Maynard Keynes over 200 years ago.

a.I& III only

b.I, II, & III only

c.II& IV only

d.IV only