Which Example Describes the Set-Up of a Controlled Experiment

Which example describes the set-up of a controlled experiment?

A) Ten subjects receive a new drug and another ten subjects receive a sugar pill.
B) Twenty subjects with knee pain receive the same treatment to relieve joint pain.
C) A doctor treats one subject for a disease and observes how quickly the patient recovers.
D) Researchers collect lifestyle data from fifty questionnaires submitted by subjects with the same disease.
E) Fifteen subjects with the common cold take a cold medicine and answer questions about its effects.