Why do individuals and governments support free trade agreements?
a. supporters of free trade believe an increase in tariffs and subsidies is good for all countries.
b. supporters of free trade feel that government regulations are necessary in trade environments.
c. free trade allows a group to focus on one type of production and become good at it.
d. free trade raises costs because of heightened competition.

I think the answer is, a.Supporters of free trade believe an increase in tariffs and subsidies is good for all countries. 
Ha-Joon Chang explained that high tariffs are based on high technological developments. Developed countries have higher technology because they are the creators of the technology. Developing countries give better and competitive value with products based on their development. On the other hand, underdeveloped countries need to improve their product and advance themselves.