The Berlin Blockade was:

a. a barrier erected by Allied forces in postwar Berlin to shield them from angry protests of starving residents.

b. a means for the United States to justify its threat to mobilize Allied forces stationed in Turkey.

c. erected because the United States threatened to invade the Soviet Union.

d. the reaction by the Soviet Union to the establishment of a separate currency in western Berlin's occupied zones.

e. a temporary defensive measure by the United States that was soon taken down.

D

Explanation:

According to Wikipedia, The Berlin Blockade (24 June 1948 - 12 May 1949) was one of the first major international crises of the Cold War. During the multinational occupation of post-World War II Germany, the Soviet Union blocked the Western Allies' railway, road, and canal access to the sectors of Berlin under Western control. The Soviets offered to drop the blockade if the Western Allies withdrew the newly introduced Deutsche Mark from West Berlin.

It was an attempt in 1948 by the Soviet Union to limit the ability of France, Great Britain and the United States to travel to their sectors of Berlin, which lay within Russian-occupied East Germany

Among the options shown here:

d. the reaction by the Soviet Union to the establishment of a separate currency in western Berlin's occupied zones.

Explanation:

France, Great Britain and the United States, the Western allies, announced on June 7, 1948, that they'd go on with the creation of West Germany. The Soviet Union did not agree with the idea and started to block terrestrial access to the German capital since June 24. The US and its allies launched an airlift to provide supplies to the encircled parts of Berlin under Western control. It lasted around a year.