Answer:
The answer is D. a placebo effect.
Explanation:
Placebos can be described as "fake" medication or treatment which intends to appear as real. Hence, the placebo effect occurs when a person affirms that he was a affected in any particular way, while there was no reason for that to happen.
For example: a person is asked to take a cup of "very high-caffeine coffee" and describe his symtpoms. The person then states that he feels very alarmed, and that his heart is racing. If at the end it's revealed that it was actually decaf coffee, it's likely the person was under the placebo effect.