The correct answer is C. tense.
Indeed, although there were several instances of hostilities in the ex-Soviet republics (namely between Armenia and Azerbaijan), they cannot be compared to the hostilities of an all-out war. The first to leave were the six countries of Eastern Europe that made part of the Warsaw pact which were not part of the Soviet Union but were satellite states.
There were violent incident in Georgia, Moldova, Ukraine, Belarus and other Central Asian republics. The Baltic countries broke away in 1990 but were still occupied. Soviet troops tried to suppress independence movements in the Baltic states. In 1991 there was a Communist coup d’état attempt that was thwarted by the civil society. Ukraine and Belarus broke away and the Soviet Union was dissolved. On December of the same year Gorbatchev resigned as the last president of the USSR and gave power to Boris Yeltsin.