A study testing the effect of caffeine on mental performance invited zoo adult participants for an experiment. These 290 individuals were selected by taking random samples of 5D people from each of the following groups: 1} men who did not drink coffee. 2] women who did not drink coffee, 3] men who regularly drank coffee and 4] women who regularly drank coffee. What type of sampling method is this? D a. Convenience sampling. O h. Voluntary sampling. O c. Multistage sampling. 0 d. Simple random sampling. 0 e. Stratified sampling