According to research described in the text, about what percent of married people in the U. S. today have sex at least twice a week?

Epigenesis is a process by which monozygotic twins tend to

A. show more differences as they get older. B. become more alike as they get older. C. show little impact from environmental factors as they age. D. demonstrate nearly total similarity throughout life regardless of the environment.

Conditions that would increase the likelihood of a negative outcome are

A. social resources. B. risk factors. C. environmental perceptions. D. genetic influences.