Answer: Gender-typing
Explanation: Gender typing is the method through a child is able to become aware about his gender so that it can further help his/her to adapt the behavioral attributes, features ,values etc from the same gender persisting individuals.
According to the situation mentioned in the question, the response obtained from the 3 to 4 years boys and girls about the male and female dolls display that they identify general activities performed by the males and females such as cooking is usually done by females and playing with truck is done by males.Thus, they show the gender-typing characteristic.