Every SINGLE person. Every person on bored that were not in a relationship died. The two that are in a relationship, did not die.
With brain teasers like this, you have to think outside of the box.
Experiments. ...
Surveys. ...
Questionnaires. ...
Interviews. ...
Case studies. ...
Participant and non-participant observation. ...
Observational trials. ...
Studies using the Delphi method.