Research on social factors and the risk for PTSD focuses primarily on the nature of the trauma, the individual's level of exposure to it, and __________________

Clouding of the crystalline lens of the eye is known as

A. vascular sclerosis B. senile macular degeneration C. senile miosis D. cataracts E. presbyopia

Which schedule of reinforcement is the most effective for initially developing and strengthening a behavior?

a) Continuous b) Fixed ratio c) Variable ratio d) Variable interval