A) December 1991

Explanation:

In order to understand why December 1991 is the correct answer, it is important to have a brief background on the events leading up to the disbandment of the Soviet Union.

1. The Fall of the Berlin Wall:
- The Berlin Wall, which symbolized the division between East and West Germany, fell on November 9, 1989.
- This event marked a significant turning point in the history of the Soviet Union as it highlighted the weakening of the communist regime and the desire for democratic reforms.

2. Gorbachev's Reforms:
- Mikhail Gorbachev, the General Secretary of the Communist Party of the Soviet Union, introduced a series of reforms in the late 1980s, known as perestroika (restructuring) and glasnost (openness).
- These reforms aimed to revitalize the Soviet economy and promote transparency and political participation.
- However, they also inadvertently fueled nationalist sentiments and demands for greater autonomy from the Soviet republics.

3. Declarations of Independence:
- In 1990, the Soviet republics of Lithuania, Latvia, and Estonia declared their independence from the Soviet Union.
- This was followed by other republics, including Russia, Ukraine, and Belarus, expressing their desire for greater sovereignty.

4. August Coup:
- On August 19, 1991, a group of hardline Communist Party members attempted to overthrow Gorbachev's government in what is known as the August Coup.
- Boris Yeltsin, the President of the Russian Soviet Federative Socialist Republic, played a crucial role in resisting the coup and rallying public support.
- The coup ultimately failed, further weakening the authority of the Soviet Union.

5. Belavezha Accords:
- On December 8, 1991, the leaders of Russia, Ukraine, and Belarus met in the Belovezhskaya Pushcha, a forest reserve in Belarus.
- They signed the Belavezha Accords, which declared the Soviet Union as "non-existent" and established the Commonwealth of Independent States (CIS) as a successor entity.
- The CIS initially included nine of the fifteen former Soviet republics, and its creation effectively marked the disbandment of the Soviet Union.

In conclusion, the correct answer is a) December 1991, as it corresponds to the signing of the Belavezha Accords and the official disbandment of the Soviet Union.