The iClicker part after Lecture 3 was cut off. What is the correct answer for the iClicker questions in lecture 3?
The correct answer is D. The terms of trade move against the fast-growing country whose export sector improves productivity. This terms-of-trade change spreads the income gains worldwide (A), cannot make the trade partners worse off (C), but can cause immiserizing growth to the growing country itself (B).

The iClicker part after Lecture 4 was cut off. What is the correct answer for the iClicker questions in lecture 4?
The correct answer is D. In each country, the relatively abundant factor gains from free trade, so neither answer A nor answer B follows with necessity (and therefore both are false). The gains for each country as a whole are strictly positive if the two countries differ, so winners can always more than compensate losers but free markets do not necessarily provide the compensation, so C is wrong.

Do the sources for external economies of scale imply that the respective industry in the host country has a high competitiveness?
This is correct. While competitiveness is not a helpful concept for the pattern of international trade (which is determined by comparative advantage), competitiveness is a useful measure of productivity. An industry with external economies of scale that has grown large with time will exhibit low average cost, hence both its productivity will be high (its competitiveness strong) and, since no other country has comparable average cost, the industry will also have the comparative advantage (and complete specialization will result). Industries that exhibit external economies of scale are industries that naturally cluster; car manufacturing may be a historic example (though arguably not a useful one in modern times), biotechnology (San Diego) and computing (Silicon Valley) are present-day examples. (Agriculture probably never showed external economies of scale.)

For the absence of an infant industry from a late-comer country, what if we just assume that a poor country has a relative lack of high-skilled workers or its respective industry just faces high transport costs for exports?
Assumptions like these could explain why a country has a comparative disadvantage in the given industry, but under common conditions (constant or decreasing returns to scale with two or more factors of production in particular), there should be incomplete specialization. The fact that there is no production at all in the given country suggests other forces, such as external economies of scale.

How do Export Promotion (of an infant industry) and Infant-industry Protection differ, or are they equivalent?
Export Promotion is a policy that subsidizes an industry's exports. Infant-industry Protection is a policy that imposed a tariff on imports that compete with a domestic industry's products. Both policies can achieve a reversal of history and attract an industrial cluster with external economies of scale to the country. However, the policies are not equivalent. Infant-industry Protection will only succeed if domestic demand is sufficiently strong, Export Promotion can succeed even if the country has small domestic demand.

When factor endowments change in the Heckscher-Ohlin model (such as through upskillin), how can it be that the slope of the production arrows changes?
For given worldwide prices of final goods, factor incomes (wages) are given and hence the slopes (factor intensities) of production arrows in the Edgeworth box are given. The length of the arrows is variable and must be such that the arrows touch each other tip to tip. When factor endowments change the shape of the Edgeworth box, then the arrows need to start out from their respective new origins.

In the Edgeworth box for the Heckscher-Ohlin model, why is an increase in the high-skill intensities (the H/L proportions), that is the slopes of the production arrows, associated with a decline in the relative factor incomes (wages) of high-skilled workers w_H/w_L?
The factor intensities (slopes of the production arrows) reflect relative labor demand of the respective industries. If we find, through geometric construction of labor-market equilibrium, that the production arrows change slope in a way that reflects an increase in the high-skill intensity (the H/L proportion) then it must be the case that, in the background, employers are facing relative wages that induce them to demand relatively more high-skilled labor. Concretely, the relative wage of high-skilled workers w_H/w_L must have fallen if all industries choose to employ relatively more high-skilled workers.