Hunter wants to prove to his parents that playing computer games while he studies for tests will him get better grades. he decides to ask 30 of his friends if they play computer games while they study for their tests and what their grades are. he finds that his friends who have high grades also play computer games while they do their homework. he tells his parents that he has proven that playing games while studying for tests will cause his grades to improve. what mistake has hunter made? a - he did not use a random sample, and he tried to show cause and effect with an experiment. b - he did not use a random sample, and he tried to show cause and effect with an observational study. c - he did not separate his friends into different groups, and he didn't apply a treatment. d - he did not separate his friends into different groups, and he used a survey to collect data.