Answer:
a. fixed price
Step-by-step explanation:
a. fixed price contract:
The vendor will be paid a fixed payment regardless his time spending. Thus the vendor will try to complete work as soon as possible, then he can receive his payment/ incentive for completed work.
b. time and materials contract:
The vendor will be paid based on time spent and material used. This contracts are normally used in construction.
c. retainer contract:
The vendor will be paid in advance for professional work to be specified later.
d. cost plus contract:
The vendor will be paid for all of its expenses, plus additional margin for its profit.