What 1960s Event Brought Piaget's Theory into the Mainstream of American

What 1960s event brought Piaget's theory into the mainstream of American science?

A) The end of the Cold War
B) Woodstock, which opened up the society to the acceptance of alternative ways of thinking
C) Flavell's summary of Piaget's work that was published in English
D) Piaget's death, which focused attention on his life's work