Question:
Who was the chair of Volkswagen Group in Sep, 1974?

Context:
 Josef Rust is the chair of Volkswagen Group from Jan, 1966 to Jan, 1974. 
 Hans Dieter Pötsch is the chair of Volkswagen Group from Jan, 2015 to Dec, 2022. 
 Hans Birnbaum is the chair of Volkswagen Group from Jan, 1974 to Jan, 1979. 
 Klaus Liesen is the chair of Volkswagen Group from Jan, 1987 to Jan, 2002. 
 Berthold Huber is the chair of Volkswagen Group from Jan, 2015 to Jan, 2015. 
 Karl Gustaf Ratjen is the chair of Volkswagen Group from Jan, 1979 to Jan, 1987. 
 Ferdinand Piëch is the chair of Volkswagen Group from Jan, 2002 to Jan, 2015.

Answer:
Hans Birnbaum