Final answer:
A double-blind experimental design is a method that psychologists can use to avoid self-fulfilling prophecies in their research.
Step-by-step explanation:
One method a psychologist could use to avoid self-fulfilling prophecies in their research is a) Double-blind experimental design. In a double-blind experiment, both the participants and the researchers are unaware of which group is the experimental group and which is the control group. This helps to minimize bias and ensure that the results are not influenced by the researchers' expectations or the participants' beliefs.