What is the "supreme law of the land" and how does it affect what states can do?

Well, that depends on which "land" you're talking about.

If it's the United States of America, then the Constitution is the supreme law of the land.

The Constitution lays out the structure and powers of the federal government in great detail.  

Then it says that any powers not specifically reserved for the federal government belong to the states.  

c. as a force against soviet invasion of afghanistan

answer is 1935

because gandhi led a march the sea in 1930 and 5 years later he did it again