Which type of contract requires that the buyer keeps the tightest labor/material cost control?

A. Cost Plus Percentage of Costs

My answer to this question is option A

Thanks for your invitation. It is the cost plus the percentage of costs.

The most suitable option is

A. Cost Plus Percentage of Costs

Answe is  A. Cost Plus Percentage of Costs...................

B. Firm Fixed Price Plus Incentive

My opinion is that the answer is C

A service level agreement (SLA) will provide an understanding between the supplier and customer on the agreed outputs and costs. This in essence provides the 'benchmark' levels for the labour and material costs. The aim from this point for the service provide, is to maximise efficiencies for the supplier business by continually measuring and analysing the systems again the benchmarks and subjecting them to CI analysis.