The correct answer is: A. evaluate variable driver.
A variable driver is a factor that causes a cost to change in direct proportion. For example, the number of units produced is a variable driver for the cost of direct materials. When the number of units produced increases, the cost of direct materials also increases.
The other options are incorrect because they are not factors that cause a cost to change in direct proportion. A cost driver is a factor that causes a cost to change, but not necessarily in direct proportion. A price driver is a factor that causes the price of a product or service to change. A demand driver is a factor that causes the demand for a product or service to change.
In quantitative analysis of estimating cost function, the last and foremost step is to evaluate variable driver. This is because the variable driver is the factor that has the most direct impact on the cost. Once the variable driver has been evaluated, the other factors can be evaluated to determine their impact on the cost.