Answer
Imitating her vocal and facial expressions.
Step-by-step explanation
Synchrony encompasses both the mother's and the child's responsivity and their emotional capacity to respond each other.For Victor and Rosa want to enhance their synchrony with their 6-month-old daughter they need to match their behaviors, emotional states and biological rhythms between them as parents and the infants because together that forms a single relational unit.The best thing they can do is by Imitating her vocal and facial expressions.