A unit-price contract pays the contractor based on measured quantities of work completed at predetermined rates (e.g., dollars per cubic metre of excavation, per metre of pipe installed, per tonne of material). This structure is used when total quantities may be uncertain at contract award, but units can be clearly defined and measured. Therefore, the owner pays a stipulated amount for each unit or section of work performed, matching option B. In a cost-plus contract (A), the owner reimburses actual costs and pays an additional fee (fixed or percentage) for overhead/profit; payment is not tied to a fixed unit schedule in the same way. In a fixed-price (lump sum) contract (C), the contractor is paid a total agreed amount for the whole scope, regardless of actual unit quantities (subject to change orders). Design-build (D) describes a project delivery method where one entity provides both design and construction; compensation can be lump sum, cost-plus, or unit-rate, so it is not defined by unit payment. Hence, B is correct.