Placebo Effects Make It Difficult to Draw Causal Conclusions Because

Placebo effects make it difficult to draw causal conclusions because we can't tell whether:

A) it is the treatment or participants' expectations that are responsible for the results.
B) random sampling or random assignment is the appropriate procedure.
C) it is the treatment or the experimenters' behaviours that are responsible for the results.
D) it is the independent variable or the dependent variable that is responsible for the results.