Define: probability sample a) people who choose themselves for a sample by responding to a general appeal. b) population is divided into similar groups and a SRS is chosen from each group. c) choosing the individuals easiest to reach. d) using extraneous factors to create similar groups. e) gives each member of the population a known chance to be selected. f) directly holding extraneous factors constant. g) the explanatory variable(s) in an experiment. h) successively smaller groups are selected within the population in stages. i) every possible sample of a given size has the same chance to be selected.