I think it is a, correct me if im wrong
the were several reasons for USSR decline.
1. the Economic Breakdown. USSR could not manage the economy well it put a lot of burden on its slow growing economy. their expenditure were more then their revenues. it was in proxy wars in various regions which proved costly to it.
2. Arms and Nuclear Race. USSR was in competition with USA in arms and nuclear race which was very expensive at that time with not developed technology. it burdened the economy more. it was not a success at first, many attempts were made to get success
3. Ideology. USSR's Ideology was the other reason for its decline. because their policies were very rigid and harsh. the decisions were carried out single highhandedly supreme leader. ideology (Communism) was very harsh and repressive.
4. harsh control and brutal policies lead to weak control of the other States so in DEC,1991 Soviet Union disintegrated into 15 countries.
