Answer:
Option B. We have assumed constant returns to scale.
Step-by-step explanation:
Constant returns to scale occur when increasing the number of inputs leads to a proportional increase in the level of output. In other words constant returns to scale is when an increase in inputs cause an equivalent increase in output.
Therefore in the scenario above, we have inaccurately assumed constant returns to scale, the is because as more inputs are added, it will get to a point where there will be less than proportionate increase, which means the extra resources added will not produce an equivalent level of output. This is the point of diminishing returns.
When this point is reached and a decrease in production is being experienced, free trade between both nations will not be as smooth as before, and each nation will start to reserve more of its products.