In each of the following studies, which variable is the independent variable and which is the dependent variable?
(a) A study comparing a group given two different kinds of medication on their level of anxiety.
(b) A study looking at heart rate change while watching one of three kinds of movies (horror movie, love story, or comedy).
(c) A study of number of touches between two infants playing in the same room, comparing when their mothers are present versus when their mothers are not present.