At Nevu Systems Inc.$\text{'}$s office, Nathan's workstation is next to Karen's. One day, Nathan overhears Karen's supervisor, Paul, say to Karen that women should just stick to being homemakers. Karen files a complaint of gender discrimination with the Equal Employment Opportunity Commission $($EEOC$).$ After the investigation and the EEOC's ruling in Karen's favor, Nathan is ill$-$treated at work simply for testifying on her behalf during the trial. Which of the following is true?

Nathan can prove a constructive discharge claim.

Nathan cannot sue his employers because he is an at$-$will employee.

Nathan can prove a case of retaliation against his employer.

Nathan cannot sue his employers because he is not in the same protected group as Karen.