Antarctica would be the continent that is difficult to connect to via trade routes, but since it is not listed in your options, Europe, North America, Asia, and Africa are all generally accessible via existing trade routes. However, if we are to choose based on potential logistical challenges, then Europe and Africa could be considered relatively easier compared to North America and Asia due to geographical distances and the presence of large oceans.
If you need a specific answer from your options, please provide clarification or indicate the context of the question.