B
He thought that mental illness occurred when the four humors were in proper balance
Hippocrates believed that the body has four bodily fluids that directly affect health and personality. Also he suggested that all diseases, including mental illness, have natural causes and he separated medicine from superstition, which is why he´s called "the father of medicine".
So, the answer that is not true about Hippocrates is option B: He thought that mental illness occurred when the four humors were in proper balance.