A randomized, controlled experiment investigated this question using a random sample of 540 adult males as subjects. 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 for 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. Which of the following is an explanatory variable in this study? Check all that apply. Group of answer choices Blood pressure after the study Type of drug given Type of diet Difference in the two measurements of blood pressure Blood pressure before the study