Quimby, Age 15 Months, Looks to Her Mother to See

Quimby, age 15 months, looks to her mother to see if she should be afraid of the stranger who has come to her home. Quimby relaxes when she sees her mother smiling and speaking to the stranger in a calm voice. Quimby is engaging in:

A) social checking.
B) social repetition.
C) social referencing.
D) social validation.