A recent study of perfect pitch -- the ability to identify the pitch of an isolated musical note -- found that a high percentage of people who have perfect pitch are related to someone else who has it. Among those without perfect pitch, the percentage was much lower. This shows that having perfect pitch is a consequence of genetic factors. Which one of the following, if true, most strengthens the argument? ['People who have relatives with perfect pitch generally receive no more musical training than do others.', 'All of the researchers conducting the study had perfect pitch.', 'People with perfect pitch are more likely than others to choose music as a career.', 'People with perfect pitch are more likely than others to make sure that their children receive musical training.']