The Following Examples Are the Independent / Predictor Variables in Proposed

The following examples are the independent / predictor variables in proposed studies. Based on these variables, which of the following most likely reflect(s) a type of "true" experimental design? (circle all that apply)

A) 2 (mood induction: happy, sad) x 3 (room temperature manipulation: hot, temperate, cold)
B) 2 (height: tall, short) x 4 (geographic region: West, South, Northeast, Midwest)
C) 3 (personality: introvert, mixed, extrovert) x 2 (adrenaline dosage: 0 cc, 10 cc)
D) 2 (pretest presented: yes, no) x 2 (manipulated seating: sat, stood)