A branch manager of a rental car company set a goal to increase customer satisfaction ratings. Thus, she authorizes additional price discounts. Customer satisfaction ratings increase overall, but the manager finds that $20\%$ of its "highly satisfied" customers were also unprofitable. This group of highly satisfied but unprofitable customers represents the company's $\_\_\_\_\_\_\_\_.$

A$.$

star customers.

B$.$

dealers.

C$.$

lost causes.

D$.$

vulnerable customers.

E$.$

free riders.