Diana wants to see if heat causes happiness. she asks 100 participants to come to the laboratory, and as they walk in, she asks each person to choose a warm booth or a cool booth. on the basis of their choices, participants spend 20 minutes in one or the other booth before rating their levels of general happiness. what's wrong with diana's experiment? a) she didn't choose an independent variable. b) she didn't expose participants to both the warm and cool booths. c) she didn't randomly assign participants to the experimental and control groups. d)she didn't measure a dependent variable.