Penelope and Phoebe are sisters who have a system to warn each other of their parents' moods and help stop each other's behavior that could make their parents yell at them. This alliance is called a:

Question

Quizplus · Accepted Answer

The term "sibling underworld" refers to a secretive or private system of communication and support between siblings, often to manage or cope with parental behavior.

Penelope and Phoebe Are Sisters Who Have a System to Warn