Which sentence from Passage 1 BEST supports the idea that birth order is associated with certain personality traits?

1) Things such as changes in family structure and parenting styles may mean that not everyone will fit the mold.

2) Middle children, however, exhibit a wider variety of qualities.

3) Birth order relates to where a person falls in the order of births in the family.

4) Firstborns are overrepresented in positions associated with very high levels of achievement.