Which of the following is correct in describing a master-servant relationship for purposes of tort liability?

A debt collection agent whose schedule is different every week is a servant of the debt collection agency.

An attorney with a law firm who spends 80% of her time working with only one of the firm's clients is a servant of the client.

A nurse who rotates working for different hospitals in need of extra staffing is a servant of each hospital because the hospitals control the working hours.

A traveling sound technician who works for a concert production company is a servant of each artist performing in each city.