D. The two countries share a border, making it easy to transport goods.
Explanation:
The presence of the long border between these countries emphasis peace and security in form of the international trade. As Mexico is the biggest trading partner of the unites states its die to the fact they are demographically connected with one another and almost about three-quarters of trade have been between them, sharing similarities.
In my opinion is that all the research I did led me too the fact that he wrte this in his resignation speech. Thats probably why he says "Through to its conclusion"
