Parents in the United States Generally Label the End of Infancy

Parents in the United States generally label the end of infancy as the "terrible twos" because:

A) their children can now be held responsible for their own actions because the children can tell right from wrong.
B) children at this age become sensitive to adult standards.
C) of their children's growing independence and the dwindling of their own control over them.
D) their children have gained reason.