Randomized, controlled experiments investigate this questions using random sample of 540 adult males as subject. At the beginning of the study, researchers measured the blood pressure of all the subjects. Each subject was given a month's supply of either Drug A, Drug B or a placebo, then was assigned to be on either a low-fat diet or a low-salt diet on that month-long period. At the end of the month the researchers measured the blood pressure of each subject again, and compared the two blood pressure readings.1.)How many different groups are there altogether in this study?2.)Which of the following is/are the explanatory variable(s) in this study?(choose all that applies)a. blood pressure before the studyb. blood pressure after the studyc. difference in the two measurements of blood pressured. type of drug givene. type of diet