The correct answer is B.
The Berlin blockade was performed by the URSS in 1948 and lasted for approximately one year.
The city of Berlin had been divided in four sectors, exactly in the same manner that the whole German territory was divided and splitted among the victorious Allied countries after WWII. US, UK and France unified their territories and created the Federal Republic while URSS created the German Democratic Republic on the Eastern the side, which remained independent from the other three . The city of Berlin was divided in four as well, but the city was actually embodied within the Eastern region of Germany under the control of the Soviet Union.
This is why the URSS could block supplies and impede ground communications with West Berlin, the area of the city controlled by US, UK and France. The so-called Berlin airlift was organized to acess this area of the city by plane, in order to bring supplies.
The correct answer is B.
The Soviets, fearing massive exodus of people escaping to the West, closed off the western sectors of Berlin. They halted all the road traffic from west to east and barred all barge and rail traffic from entering West Berlin, thus creating the Berlin blockade.
The Allies decided to supply their sectors of Berlin from the air. This project, known as operation Berlin Airlift or Berlin Air Bridge lasted more than a year.
Hundreds of American, British and French cargo planes ferried provision from Western Europe to the airfield in Tempelhof ( in the American sector ), Gatow ( in the British sector ), and Tegel ( the French sector ).