Read this and answer the question. If the question is unanswerable, say "unanswerable".

On July 1, 1985, Gorbachev promoted Eduard Shevardnadze, First Secretary of the Georgian Communist Party, to full member of the Politburo, and the following day appointed him minister of foreign affairs, replacing longtime Foreign Minister Andrei Gromyko. The latter, disparaged as "Mr Nyet" in the West, had served for 28 years as Minister of Foreign Affairs. Gromyko was relegated to the largely ceremonial position of Chairman of the Presidium of the Supreme Soviet (officially Soviet Head of State), as he was considered an "old thinker." Also on July 1, Gorbachev took the opportunity to dispose of his main rival by removing Grigory Romanov from the Politburo, and brought Boris Yeltsin and Lev Zaikov into the CPSU Central Committee Secretariat.

Who was responsible for Shevardnadze's membership?
Gorbachev