A Researcher Conducting a Study on the Effectiveness of a New

A researcher conducting a study on the effectiveness of a new prescription medication gives the actual medication to a group of people. A second group of participants are told they are receiving the medication but instead are given an inert sugar pill. Though the
Drug is found to be effective for the people who actually took it, a sizeable percentage of the people given the sugar pill also improve. The improvement of this second group is most likely due to:

A) experimenter expectancy effects.
B) the placebo effect.
C) sampling bias
D) social desirability bias.