Question:
Who was the head of state of German Democratic Republic in Apr, 1974?

Context:
 Erich Honecker is the head of the state of German Democratic Republic from Oct, 1976 to Oct, 1989. 
 Wilhelm Pieck is the head of the state of German Democratic Republic from Oct, 1949 to Sep, 1960. 
 Egon Krenz is the head of the state of German Democratic Republic from Oct, 1989 to Dec, 1989. 
 Walter Ulbricht is the head of the state of German Democratic Republic from Sep, 1960 to Aug, 1973. 
 Willi Stoph is the head of the state of German Democratic Republic from Oct, 1973 to Oct, 1976. 
 Manfred Gerlach is the head of the state of German Democratic Republic from Dec, 1989 to Apr, 1990. 
 Sabine Bergmann-Pohl is the head of the state of German Democratic Republic from Apr, 1990 to Oct, 1990.

Answer:
Willi Stoph