The term "sex" and "gender" are often used interchangeably. But "sex" more properly refers to biological differences of male and female, while "gender" refers to society' s construction of a system that identifies what is masculine and feminine. Unlike the set of characteristics defining biological sex, the set of traits that are associated with gender does not sort people into two nonoverlapping groups. The traits characterize people in a complex way, so that a person may have both "masculine" and "feminine" traits. Which one of the following statements best expresses a main point of the argument? ['Distinctions based on gender are frequently arbitrary.', 'Society rather than the individual decides what is considered proper behavior.', 'The terms "sex" and "gender" are not properly interchangeable.', 'Gender traits are not determined at birth.']