Billy Runs an Accounting Firm

Billy runs an accounting firm.He has three full-time employees who are paid an annual salary of $135,000 each.For 4 weeks during the tax preparation season,Billy hires additional staff on a temporary basis to meet the surge in demand for his firm's service.Billy must also pay a premium for professional liability insurance for the whole firm every month.For Billy's firm,________.

A) the full-time employees and the liability insurance are fixed inputs
B) all employees, full-time and temporary, are variable inputs
C) the liability insurance is a variable input
D) all inputs are variable