Though Jean Piaget Assumed That Children Under the Age of 6

Though Jean Piaget assumed that children under the age of 6 to 7 years old have great difficulty understanding other people's mental states, recent studies have suggested that children have some understanding that other people's perspectives can differ from their own by the age of _.

A) 3 to 4 years
B) 2 years
C) 5 years
D) 2 to 3 years