Question:
Who was the chair of Communist Party of the Soviet Union in Dec, 1984?

Context:
 Yuri Andropov is the chair of Communist Party of the Soviet Union from Nov, 1982 to Feb, 1984. 
 Mikhail Gorbachev is the chair of Communist Party of the Soviet Union from Mar, 1985 to Aug, 1991. 
 Joseph Stalin is the chair of Communist Party of the Soviet Union from Apr, 1922 to Sep, 1953. 
 Volodymyr Ivashko is the chair of Communist Party of the Soviet Union from Aug, 1991 to Nov, 1991. 
 Leonid Brezhnev is the chair of Communist Party of the Soviet Union from Oct, 1964 to Nov, 1982. 
 Konstantin Chernenko is the chair of Communist Party of the Soviet Union from Feb, 1984 to Mar, 1985. 
 Nikita Khrushchev is the chair of Communist Party of the Soviet Union from Sep, 1953 to Oct, 1964.

Answer:
Konstantin Chernenko