Placebos A Placebo Is Any Kind of Drug, Procedure, or Treatment

Placebos
A placebo is any kind of drug, procedure, or treatment that does not have legitimate medicinal properties. Placebos do not contain any sort of active ingredient meant to treat an illness or injury. Placebo pills, for example, might be made out of sugar or corn starch. However, even though placebos contain no medicine whatsoever, people who take them often experience reactions that cannot possibly be triggered by the substances in the pills themselves. This is known as the placebo effect.
In one study of the placebo effect, volunteers were given a starch pill and told that it was a stimulant similar to caffeine. These volunteers reported feeling more alert and slightly jittery. They also showed an increased heart rate and a spike in blood pressure. Researchers then gave the exact same placebo pill to a different group of people, this time telling them that it was a depressant. The second group of participants reported feeling drowsy and sluggish, and showed a reduced heart rate and lowered blood pressure.
Researchers use placebos to evaluate the effectiveness and possible side effects of new drugs. For example, during a study for a drug to treat depression, half of the participants might be given the actual drug while the other half are given a placebo. None of the participants know whether or not they are taking the real drug or the placebo. Researchers can then compare the results between the two groups to determine whether or not the drug produces the desired results and examine the side effects.
What is the primary purpose of this passage?

A) To inform the reader about placebos and explain why they are used.
B) To compare the experiences of two volunteer groups in a study regarding the placebo effect.
C) To warn the reader of the dangers associated with taking ineffective pills.
D) To entertain the reader with stories regarding what to expect when volunteering for a study.