3. Which nation forms Canada southern border? * Mexico
Russia
United States
Greenland

It is the United States.

As you can see here, the United States is south of Canada.

the first one is d and the second a

the secretary of state, appointed by the president with the advice and consent of the senate, is the president's chief foreign affairs adviser. the secretary carries out the president's foreign policies through the state department and the foreign service of the united states.