In a study where a series of composite faces were made from several individuals, the composite ...

In a study where a series of composite faces were made from several individuals, the composite images were rated as more attractive than almost all of the individual faces used to produce the composite image. What might this suggest?
 
  a. The average look of a population represents the optimal design of physical traits.
  b. The people who made up the individual components of the composite face, were found to be less fertile than the average population.
  c. People with both male and female facial characteristics, are perceived as highly attractive.
  d. Since composite images are commonly used in advertisements, our perceptions of beauty have adapted to current marketing practices.