A. They reduce the workforce and encourage foreign investment.
B. They create the basis for poverty.
C. They make it impossible for democracy to prevail.
D. They force the government to impose high taxes on everyone.
Lack of education usually means lack of innovation. You can dream up ideas, but it's not going to help much if people don't know how to implement them. High national debt would mean that other countries are less likely to want to loan you money which means you don't have the funds for research and development, and buying the materials that are needed, but not produced by your country.
Trade barriers come in many forms.
Physical - You are in a location that makes it difficult for shipment of needed supplies to be brought in or traded out (ex: sahara desert, north pole).
Political - Your country has an embargo against it that limits trade with other countries.
Cultural trade barriers - the customs of a particular country prohibit trading certain types of products from outside sources (ex: It goes against some religions to bring in medicines from outside sources).
Language - You may have a language that is very hard to translate, and thus empede trade (ex: chinese due to it's many dialects, tends to be very difficult to translate).
Finally, lack of technology may limit being able to do trades with other countries (ex: many developing countries do not have a well made road system to help get supplies to people who live deep in the mountains)
