In which research design are age differences and cohort differences hopelessly tangled?

If a researcher were to observe women exercising and then men exercising and compare these groups, why would this not be considered an experiment?

a. The experimenter is not manipulating anything. b. The study is biased. c. There is no prior evidence that gender is related to one's preferred type of exercise. d. An experiment must involve at least three different conditions.

The textbook suggests that the best way to characterize nature-nurture issues is to suggest that the two ____________. That is, genes and environment work both separately and together, and sometimes they influence or change one another

Fill in the blank(s) with the appropriate word(s).