Mary beth is running an experiment and wants to make sure she has randomly assigned her 40 participants to the two conditions. which of the following methods of forming groups would give her random assignment? 1. assign the first 20 to show up to the first group and the second 20 to the second group. 2. post two sign-up sheets: 9 a. m. for the first group and 2 p. m. for the second group. 3. participants with names in the first half of the alphabet are in the first group; the second half of the alphabet are in the second group. 4. flip a coin as each participant arrives: heads indicates assignment to the first group, tails indicates assignment to the second group.