In an experiment, researchers played a series of musical intervals -- two-note sequences -- to a large, diverse group of six-month-old babies. They found that the babies paid significantly more attention when the intervals were perfect octaves, fifths, or fourths than otherwise. These intervals are prevalent in the musical systems of most cultures around the world. Thus, humans probably have a biological predisposition to pay more attention to those intervals than to others. Which one of the following, if true, most strengthens the argument? ['Octaves, fifths, and fourths were played more frequently during the experiment than other musical intervals were.', 'Several similar experiments using older children and adults found that these subjects, too, had a general tendency to pay more attention to octaves, fifths, and fourths than to other musical intervals.', 'All of the babies in the experiment had been exposed to music drawn equally from a wide variety of cultures around the world.', 'None of the babies in the experiment had previous exposure to music from any culture.']