Marta no longer uses a particular vending machine on campus because it has consistently failed to deliver marta's snack or soda when she inserted her money and made her selection. marta's experiment best illustrates:

a: social security and social programs

answer; i believe the correct answer is (4) flip a coin as each participant arrives,heads indicates assignment to the first group: tails indicates assignment to the second group;

answer; the best answer is (demand);