Answer:
A
Explanation:
B is incorrect because the Berlin Airlift took place between 1948 -1949; long before Gorbachev's resignation in 1991.
C is incorrect because the policies of Glasnost and Perestroika, being his own policies, directly resulted from Gorbachev's time in power, not his resignation.
D is incorrect because the fall of the Berlin Wall occurred shortly before Gorbachev's resignation. Therefore, it cannot be the effect of Gorbachev's resignation.
Thus, A is correct.
______________________________________________________
Hoped that helped! If it did, mark me Brainliest!