When did the caste system evolve into four tiered hierarchy

Which was the cause of the rise of the persian empire?

The internal combustion engine was an innovation of

What is the evidence that depression can be linked to genetic as well as environmental factors? a. all individuals in similar stressful environments do not experience depression. b. all individuals with the gene variation tied to depression do not experience depression. c. individuals with a combination of environmental stress and gene variation are more likely to experience depression d. all of the above select the best answer from the choices provided оа 0 0 0