Regarding the Big Five, most psychologists would probably agree with the statement that:

A) an individual's core traits change a lot throughout his or her lifetime.
B) important traits involved in mental disorders are included in the Big Five.
C) they only apply to people in western cultures, such as the United States and Great Britain.
D) they lie at the core of key personality variations among individuals throughout the world.

The Big Five personality traits (openness, conscientiousness, extraversion, agreeableness, and neuroticism) have been found to be consistent across different cultures and are considered to be fundamental traits that underlie personality variations among individuals throughout the world. Therefore, option D is the best choice. Option A is incorrect as although some traits may change over time, core traits tend to remain relatively stable. Option B may be true, but it is not the focus of the statement. Option C is incorrect as research has found these traits to be cross-culturally applicable.