Sickle-cell disease is a painful disorder of the red blood cells. To investigate whether the drug Hydroxyurea can reduce the pain associated with sickle-cell disease, a study by the National Institute of Health gave the drug to 150 sickle-cell patients and the placebo to another 150 patients, Neither the doctors nor the patients were told who received the drug. The number of episodes of pain reported by each subject was recorded. Answer the following questions. [2+2+2+2 pts.] . Is this an observational study or an experiment? . What is the explanatory variable? . What is the response variable? . Suggest a lurking variable that may be confounded with the number of episodes of pain reported by each subject. Edit View Insert Format Tools Table 12pt v Paragraph | B J U A Q V TV B DV