The best explanation for the collapse of the Soviet Union is A: the government spent money on the military and weapons and neglected the rest of the economy.
This militarization contributed to significant economic strain, as the Soviet leadership prioritized military expenditures over consumer goods and infrastructure, ultimately leading to economic stagnation. The excessive focus on military power, combined with other factors like political corruption, a lack of reform, and internal nationalism within various Soviet republics, played a crucial role in the dissolution of the Soviet Union in 1991.