Final answer:
Kitty and Stuart are liable for the harm caused to the strangers below on the streets due to their negligent behavior.
Step-by-step explanation:
In this scenario, Kitty and Stuart are liable for the harm caused to the strangers below on the streets. Their actions of throwing water balloons at the strangers can be considered as a negligent act. Negligence is a legal term that refers to the failure to exercise the level of care that a reasonable person would in a similar situation.
By throwing water balloons from the top of the twentieth floor, Kitty and Stuart created a potential risk of harm to the strangers below. They should have foreseen the possibility that the water balloons could injure someone or cause damage to property. Therefore, they can be held responsible for any injuries or damages resulting from their negligent behavior.