Final answer:
d. Afghanistan is the country in Southwest Asia that would have the most difficulty engaging in international trade due to being landlocked.
Step-by-step explanation:
The country in Southwest Asia that would have the most difficulty engaging in international trade due to being landlocked is d. Afghanistan.
Landlocked countries are those that do not have access to the sea, making it more challenging to transport goods and engage in maritime trade. Afghanistan is located in the heart of Central Asia and is surrounded by land on all sides, making it dependent on neighboring countries for trade through land routes.