A Dentist Hired a Janitorial Service to Clean Her Office

A dentist hired a janitorial service to clean her office every evening.The original contract called for the janitorial service to dust,mop all floors,and vacuum the rugs.After six months,the dentist decided to renegotiate the contract with the janitorial service to include cleaning the office bathroom and washing the office windows as well as the original tasks.The renegotiated contract is an example of a:

A) contingency buy.
B) modified rebuy.
C) negotiated buying system.
D) straight rebuy.
E) newbuy situation.