What Is One of the Reasons That Researchers Have Had

What is one of the reasons that researchers have had trouble agreeing about the nature of the fifth factor of the five-factor model of personality?

A) Cross-cultural researchers have been unable to study the fifth factor across many languages.
B) Different researchers use different item pools in the factor analysis of big five data.
C) Researchers using questionnaire items favor "openness to experience" as the trait label.
D) Researchers using trait descriptive adjectives favor "intellect" as the trait label.