The correct answer is B. President Kennedy's response to the construction of the Berlin Wall led the Soviet Union to believe that Kennedy would back down if confronted.
The Western reaction to the construction of the wall was slow: 20 hours passed until the appearance of military forces on the border; 40 hours until they communicated with the Soviet commander of Berlin; 72 hours until they protested at Moscow's diplomacy. There were more and more rumors that the Soviets had assured the Western allies that they would not threaten their rights. The experience of the blockade had shown the allies that West Berlin was threatened, so the construction of the wall was a material confirmation of the status quo.
Kennedy claimed that Berlin was a "free state" and sent a reinforcement brigade of 1500 men to West Berlin. The leader of the GDR Walter Ulbricht even determined the control on the part of the Border and Popular Police on the allied officers and police, which produced a strong rejection, in particular on the part of the Americans.
