Why did communism in the soviet union collapse in the late 1980s?

There were several reasons due to which the Soviet Union collapsed in the late 1980's. Firstly the defense spending of the Soviets during that period was very high and it almost bankrupted the country. This was the reason the people of Soviet Union had to suffer. The people were also angry seeing the lavishness of the people living in the Western countries. The difference in the standard of living also opened the eyes of the general people. Ultimately the people revolted against the communists and this led to the collapse of the communism in the late 1980's. Although the communists tried their best to hold on, but the people ultimately did not accept communism any more.

Ithink the answer is a.