The correct answer to this open question is the following.
The type of claim the author is making is a cause and effect because the author is saying that the Soviet Union collapsed after Russian leader Mikhail Gorbachev implemented his policies of the reformation in the country and the overspending on military commitments
The type of evidence the author should use to best support the claim is to use primary and secondary sources to include information about the two main reformations policies implemented by Gorbachev: Perestroika and Glasnost.
The author has to explain how Perestroika opened the frontiers of the USSR to welcome foreign investment, and on the other hand, how Glasnosts allowed liberties that were suppressed since Joseph Stalin's time, so Russian people started to express themselves.
These two factors can explain the split of the Soviet Unión.