Which classic philosophical school of thought held that ""all behavior is rigidly determined by natural laws""?

Answer: Stoicism

Explanation: This classical philosophical school of Hellenistic Greece was founded by Zeno of Citium. Zeno founded this philosophical school in the third century BC in Athens. The philosophy of this school is to find happiness by accepting the present moment as it is, and not allowing yourself to be controlled by desire for any pleasure or fear of pain. Also, personal ethics and constructed behaviour depend on natural laws, i. e on personal acceptance of these laws and nature in general. In this regard, we should cooperate with nature and become part of the overall natural plan by contributing to it with our participation. That is why we have to treat nature and others fairly, in order to accept and experience natural laws with such logic, and thus to build such personal behaviour.