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