Some subjects try to solve a difficult maze while sitting in a 2x3 ft room. others try to solve the same maze while sitting in a 10x12 ft room. the purpose of the study is to examine the effect of crowding on maze performance the larger room has natural light because of its two windows. the 2x3 ft room has no windows, so natural light is simulated with a special type of fluorescent light. which of the following is true?
a. the independent variable is the type of maze being used
b. whether or not windows are present is an uncontrolled extraneous variable
c. assuming random assignment is used, this study clearly has internal validity
d. the main variable is a subject variable