What Was the Primary Difference Between the Methodology Used by Freud

What was the primary difference between the methodology used by Freud and that used by 20^th century sex researchers?

A) The 20^th century sex researchers saw sex as a disease to be treated.
B) The 20^th century sex researchers observed their patients only in laboratories.
C) The 20^th century sex researchers saw sex as a measure of social progress.
D) The 20^th century sex researchers believed that sexual development ceases after childhood.
E) The 20^th century sex researchers believed that sexual development started only after childhood.