Which Is an Example of Primary Intersubjectivity

Which is an example of primary intersubjectivity?

A) A child turns her gaze toward the door when her mother looks that direction.
B) Seeing his mother's look of alarm, a child cries when approached by a large dog.
C) A child takes a turn smiling at his mother and being smiled at in return.
D) A child is upset when she is left with a babysitter while her parents go out.