A retrospective study is a scientific study that tries to determine the causes of subjects' present characteristics by looking for significant connections between the present characteristics of subjects and what happened to those subjects in the past, before the study began. Because retrospective studies of human subjects must use the subjects' reports about their own pasts, however, such studies cannot reliably determine the causes of human subjects' present characteristics. Which one of the following, if assumed, enables the argument's conclusion to be properly drawn? ["A retrospective study cannot reliably determine the causes of human subjects' present characteristics unless there exist correlations between the present characteristics of the subjects and what happened to those subjects in the past.", "In studies of human subjects that attempt to find connections between subjects' present characteristics and what happened to those subjects in the past, the subjects' reports about their own pasts are highly susceptible to inaccuracy.", "Every scientific study in which researchers look for significant connections between the present characteristics of subjects and what happened to those subjects in the past must use the subjects' reports about their own pasts.", "Whether or not a study of human subjects can reliably determine the causes of those subjects' present characteristics may depend at least in part on the extent to which that study uses inaccurate reports about the subjects' pasts."]