What was the iron curtain?
o a line of guns and canons that the soviets spread across eastern europe
o
the imaginary wall separating communist countries from democracies
o the security arrangements that stalin made to protect himself
o a powerful agreement forged at yalta at the end of world war ii

C is correct (the security arrangements that Stalin made to protect himself).

Explanation: the term "Iron Curtain"  was used for the first time by Winston Churchill in American town of Fulton (Missouri) in 1946 (so-called "Fulton Speech). At that time Churchill was a ex-prime-minister, but the phenomenon of "Iron Curtain" was quite visible even from the UK.

richard nixon led the investigation that resulted in alger hiss being convicted of prejury.

the answer here would be