Astudy is created in which the participants were randomly assigned to groups for different treatments. which best describes the reason this was done?   a. it allows us to see the true nature of any effects of different treatments.   b. it allows us to determine if the treatment effect is significantly different from the placebo effect.   c. it allows us to distinguish among the effects of different factors.   d. it allows us to use chance as a way to create groups that are similar to the population.