Which of the Following Describes an Employee Who Would Most

Which of the following describes an employee who would most likely be able to force an employer to improve work conditions?

A) Goran is the only person Hartley Construction employs who will clean debris from work sites.
B) Bill is a skillful market researcher for a marketing consulting firm.
C) Ana manages a database for a telemarketer and is the only one who understands the system she designed.
D) Karin is the only person in her office who can use the accounting software that the company bought even though it is simple to use.
E) Adam has a commercial driver's license and a twenty-year safe driving record.