Your company was given a warning from the EEOC regarding their hiring practices. Specifically, they believed that you may be illegally hiring based on surface$-$level differences. As the HR manager, you have been tasked with training the employees in charge of interviewing. Which of the following does not represent a surface$-$level difference that is illegal to be a considered when hiring?

Gender

Personality

Disability

Race

All of the above $($A$,$ B$,$ C$,$ & D$)$ represent surface$-$level differences