Which of the following is an example of an independent variable?

The independent variables in the study by Kenrick and colleagues on "computer dating"

included the a. participants' ratings of the attractiveness of the people in the photographs. b. presence or absence of a physically attractive confederate. c. participants' rankings of the desirability of a potential mate's characteristics. d. photographs of people of different levels of physical attractiveness and the descriptions of these people as being eitherhigh or low in dominance. e. participants' evaluations of their current dating relationship.

Ben has a very typical reaction to the arrival of his new baby sister. Like children everywhere, he might typically respond with:

a. great enthusiasm and joy b. jealousy c. fear d. expectations regarding being the younger sibling's mentor