Homework help please:

Researchers randomly assigned patients with severe acne to one of two treatments: the standard topical antibiotic (our control) or a new antibiotic taken orally (the treatment). Six months later an evaluation of skin problems was made by a doctor who did not know which medication subjects had been given. What is the primary advantage of random assignment of the treatment?

(a) It allows the researchers to infer that any difference in outcome was due to the treatments.

(b) It allows inference back to a population of patients with acne.

(c) It ensures that the subject doesn't know which treatment they are getting.

or (d) It ensures that the study participants are representative of the larger population.