Answer: 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.
Mainly trading but also because of sugar and cropping in the 1500s was a big money maker
